Add GitLab Code Quality report format to lint/breaking file annotations output

[doriable]

This adds gitlab-code-quality as an option to buf {lint,breaking} --error-format, e.g.

$ buf lint --error-format=gitlab-code-quality | jq .
[
  {
    "description": "Files must have a package defined.",
    "check_name": "PACKAGE_DEFINED",
    "fingerprint": "f8c457c94c905148d8a60653f612faf64f2a5a412d73a5e520e3ffceecce38b2a0602d65cda99e1f976ddb3cf36c18033bae39a27e49b4798332af33c66e8f6e",
    "location": {
      "path": "main/main.proto",
      "positions": {
        "begin": {
          "line": 1,
          "column": 1
        },
        "end": {
          "line": 1,
          "column": 1
        }
      }
    },
    "severity": "minor"
  },
  {
    "description": "Import \"google/protobuf/timestamp.proto\" is unused.",
    "check_name": "IMPORT_USED",
    "fingerprint": "2df05dc6fa275d42b75b6d944b21e8633e3ea1073ff957091020aa293711aba2635707100fef418c475e5eda8eee96c0acc980cb8ea985f3944fb83e9046f7ca",
    "location": {
      "path": "main/main.proto",
      "positions": {
        "begin": {
          "line": 5,
          "column": 1
        },
        "end": {
          "line": 5,
          "column": 47
        }
      }
    },
    "severity": "minor"
  },
  {
    "description": "Files must have a package defined.",
    "check_name": "PACKAGE_DEFINED",
    "fingerprint": "08e55d130a39cc578affe0cf1825a1acff2792e46bf98e9e7b147bc77cd19e6be59808798046548c93a87642942db7e9f88a02f8c7097ae752ea607b8116a556",
    "location": {
      "path": "test/test.proto",
      "positions": {
        "begin": {
          "line": 1,
          "column": 1
        },
        "end": {
          "line": 1,
          "column": 1
        }
      }
    },
    "severity": "minor"
  }
]

It is important to note that GitLab Code Quality report expects a single JSON array.
Based on the documentation, GitLab Code Quality report also always expects a relative
path based on the repository in the location, and if the location/path is missing, this could
result in Code Quality issues being dropped from report view. It is up to the user to ensure
that their buf {lint, breaking} invocations are configured accordingly with their repositories.
GitLab Code Quality report also always expects all fields to be present.

Fixes #3926

[github-actions]

The latest Buf updates on your PR. Results from workflow Buf CI / buf (pull_request).

Build	Format	Lint	Breaking	Updated (UTC)
✅ passed	✅ passed	✅ passed	✅ passed	Aug 5, 2025, 6:28 PM

[doriable]

Using the shake256 digest of the JSON FileAnnotation for the hash, but open to suggestions on this!