[TT-7524] [OAS] Gateway CE behaves differently from Dashboard for middleware and PATCH (#7261)

### **User description**
<details open>
<summary><a href="https://tyktech.atlassian.net/browse/TT-7524"
title="TT-7524" target="_blank">TT-7524</a></summary>
  <br />
  <table>
    <tr>
      <th>Summary</th>
<td>[OAS] Gateway CE behaves differently from Dashboard for middleware
and PATCH</td>
    </tr>
    <tr>
      <th>Type</th>
      <td>
<img alt="Bug"
src="https://tyktech.atlassian.net/rest/api/2/universal_avatar/view/type/issuetype/avatar/10303?size=medium"
/>
        Bug
      </td>
    </tr>
    <tr>
      <th>Status</th>
      <td>In Dev</td>
    </tr>
    <tr>
      <th>Points</th>
      <td>N/A</td>
    </tr>
    <tr>
      <th>Labels</th>
<td><a
href="https://tyktech.atlassian.net/issues?jql=project%20%3D%20TT%20AND%20labels%20%3D%20codilime_refined%20ORDER%20BY%20created%20DESC"
title="codilime_refined">codilime_refined</a></td>
    </tr>
  </table>
</details>
<!--
  do not remove this marker as it will break jira-lint's functionality.
  added_by_jira_lint
-->

---

<!-- Provide a general summary of your changes in the Title above -->

## Description

Updating an API with the PATCH /tyk/apis/oas/{apiId} command via Gateway
API does not trigger the Tyk vendor extension (x-tyk-api-gateway)
update, which results in the API description being out of sync or
invalid.

## Related Issue

<!-- This project only accepts pull requests related to open issues. -->
<!-- If suggesting a new feature or change, please discuss it in an
issue first. -->
<!-- If fixing a bug, there should be an issue describing it with steps
to reproduce. -->
<!-- OSS: Please link to the issue here. Tyk: please create/link the
JIRA ticket. -->

## Motivation and Context

<!-- Why is this change required? What problem does it solve? -->

## How This Has Been Tested

<!-- Please describe in detail how you tested your changes -->
<!-- Include details of your testing environment, and the tests -->
<!-- you ran to see how your change affects other areas of the code,
etc. -->
<!-- This information is helpful for reviewers and QA. -->

## Screenshots (if appropriate)

## Types of changes

<!-- What types of changes does your code introduce? Put an `x` in all
the boxes that apply: -->

- [x] Bug fix (non-breaking change which fixes an issue)
- [ ] New feature (non-breaking change which adds functionality)
- [ ] Breaking change (fix or feature that would cause existing
functionality to change)
- [x] Refactoring or add test (improvements in base code or adds test
coverage to functionality)

## Checklist

<!-- Go over all the following points, and put an `x` in all the boxes
that apply -->
<!-- If there are no documentation updates required, mark the item as
checked. -->
<!-- Raise up any additional concerns not covered by the checklist. -->

- [ ] I ensured that the documentation is up to date
- [ ] I explained why this PR updates go.mod in detail with reasoning
why it's required
- [ ] I would like a code coverage CI quality gate exception and have
explained why


___

### **PR Type**
Bug fix, Tests


___

### **Description**
- Fix removal of obsolete operations in Tyk extension during OAS PATCH.

- Add test to ensure outdated operations are deleted.

- Enhance middleware import logic for operation cleanup.

- Improve consistency between Gateway and Dashboard OAS handling.


___

### Diagram Walkthrough


```mermaid
flowchart LR
  PATCH_OAS["PATCH OAS API"] -- "Triggers" --> importMiddlewares["importMiddlewares updates operations"]
  importMiddlewares -- "Collects current ops" --> removeObsolete["removeObsoleteOperations removes outdated ops"]
  removeObsolete -- "Cleans up" --> TykExtension["Tyk Extension up-to-date"]
  default_test["Add test for obsolete ops removal"] -- "Verifies" --> removeObsolete
```



<details> <summary><h3> File Walkthrough</h3></summary>

<table><thead><tr><th></th><th align="left">Relevant
files</th></tr></thead><tbody><tr><td><strong>Bug
fix</strong></td><td><table>
<tr>
  <td>
    <details>
<summary><strong>default.go</strong><dd><code>Remove obsolete operations
from Tyk extension during import</code></dd></summary>
<hr>

apidef/oas/default.go

<ul><li>Track current operations during middleware import.<br> <li> Add
<code>removeObsoleteOperations</code> to delete outdated operations.<br>
<li> Call cleanup after updating operations.<br> <li> Use
<code>slices.Contains</code> for efficient operation checks.</ul>


</details>


  </td>
<td><a
href="https://github.com/TykTechnologies/tyk/pull/7261/files#diff-83c3a85bdd05785178ee519b05b1fe2008435dc4ae9448d72b080b5f67c491ad">+21/-0</a>&nbsp;
&nbsp; </td>

</tr>
</table></td></tr><tr><td><strong>Tests</strong></td><td><table>
<tr>
  <td>
    <details>
<summary><strong>default_test.go</strong><dd><code>Test removal of
obsolete operations from Tyk extension</code>&nbsp; &nbsp; &nbsp;
</dd></summary>
<hr>

apidef/oas/default_test.go

<ul><li>Add test to verify removal of outdated operations.<br> <li>
Ensure Tyk extension matches expected operations after update.</ul>


</details>


  </td>
<td><a
href="https://github.com/TykTechnologies/tyk/pull/7261/files#diff-ab6848f71731083885a9d7d7970faa68a6783a98477c78413ae3979cb5add7db">+28/-0</a>&nbsp;
&nbsp; </td>

</tr>
</table></td></tr></tr></tbody></table>

</details>

___

Author: MaciekMis

apidef/oas/default.go

@@ -6,6 +6,7 @@ import (
 	"net/http"
 	"net/url"
 	"reflect"
+	"slices"
 	"strconv"
 	"strings"
 
@@ -220,22 +221,42 @@ func (s *OAS) importMiddlewares(overRideValues TykExtensionConfigParams) {
 		xTykAPIGateway.Middleware = &Middleware{}
 	}
 
+	currentOperations := make([]string, 0)
+
 	for path, pathItem := range s.Paths.Map() {
 		overRideValues.pathItemHasParameters = len(pathItem.Parameters) > 0
 		for _, method := range allowedMethods {
 			if operation := pathItem.GetOperation(method); operation != nil {
 				tykOperation := s.getTykOperation(method, path)
 				tykOperation.Import(operation, overRideValues)
+				currentOperations = append(currentOperations, s.getOperationID(path, method))
 				s.deleteTykOperationIfEmpty(tykOperation, method, path)
 			}
 		}
 	}
 
+	s.removeObsoleteOperations(currentOperations)
+
 	if ShouldOmit(xTykAPIGateway.Middleware) {
 		xTykAPIGateway.Middleware = nil
 	}
 }
 
+func (s *OAS) removeObsoleteOperations(currentOperations []string) {
+	tykOperations := s.getTykOperations()
+	obsoleteOperations := make([]string, 0)
+
+	for id := range tykOperations {
+		if !slices.Contains(currentOperations, id) {
+			obsoleteOperations = append(obsoleteOperations, id)
+		}
+	}
+
+	for _, operationID := range obsoleteOperations {
+		delete(tykOperations, operationID)
+	}
+}
+
 func (s *OAS) getTykOperation(method, path string) *Operation {
 	xTykAPIGateway := s.GetTykExtension()
 	operationID := s.getOperationID(path, method)

apidef/oas/default_test.go

@@ -563,6 +563,34 @@ func TestOAS_BuildDefaultTykExtension(t *testing.T) {
 			return operations
 		}
 
+		t.Run("operations not present in new oas paths definition should be removed", func(t *testing.T) {
+			fakeOperationName := "fakeOperation"
+			fakeOperation := &Operation{
+				MockResponse: &MockResponse{
+					Enabled: true,
+				},
+			}
+			oasDef := getOASDef(true, true)
+
+			tykExtensionConfigParams := TykExtensionConfigParams{
+				MockResponse: &trueVal,
+			}
+
+			extension := &XTykAPIGateway{
+				Middleware: &Middleware{
+					Operations: map[string]*Operation{fakeOperationName: fakeOperation},
+				},
+			}
+			oasDef.SetTykExtension(extension)
+			assert.Greater(t, len(oasDef.getTykOperations()), 0)
+
+			expectedOperations := getExpectedOperations(true, true, middlewareMockResponse)
+			err := oasDef.BuildDefaultTykExtension(tykExtensionConfigParams, true)
+
+			assert.NoError(t, err)
+			assert.Equal(t, expectedOperations, oasDef.getTykOperations())
+		})
+
 		t.Run("allowList", func(t *testing.T) {
 			t.Run("enable allowList for all paths when no configured operationID in OAS", func(t *testing.T) {
 				oasDef := getOASDef(false, false)