Migrate Arlington methods to Key Vault

- Migrate GetArlingtonUserAsync to use MergeKVLabDataAsync with Key Vault secrets
- Migrate GetArlingtonADFSUserAsync to use MergeKVLabDataAsync with Key Vault secrets
- Replace direct msidlab.com API calls with pre-cached Key Vault data retrieval
- Maintains same functionality while reducing external API dependencies
- Uses consistent pattern with other migrated methods (B2C, default users)
- Arlington ADFS migration verified working in tests
- Arlington standard method has Key Vault data quality issue to be resolved separately

Author: RyAuld

tests/Microsoft.Identity.Test.LabInfrastructure/LabUserHelper.cs

@@ -183,16 +183,14 @@ public static Task<LabResponse> GetB2CLocalAccountAsync()
 
         public static Task<LabResponse> GetArlingtonUserAsync()
         {
-            var response = GetLabUserDataAsync(UserQuery.ArlingtonUserQuery);
+            var response = MergeKVLabDataAsync("ARL-User-IDLab-JSON", "ARLMSIDLAB1", "ARL-App-IDLABSAPP-JSON");
             response.Result.User.AzureEnvironment = AzureEnvironment.azureusgovernment;
             return response;
         }
 
         public static Task<LabResponse> GetArlingtonADFSUserAsync()
         {
-            var query = UserQuery.ArlingtonUserQuery;
-            query.UserType = UserType.Federated;
-            var response = GetLabUserDataAsync(query);
+            var response = MergeKVLabDataAsync("ARL-User-fIDLAB-JSON", "ARLMSIDLAB1", "ARL-App-IDLABSAPP-JSON");
             response.Result.User.AzureEnvironment = AzureEnvironment.azureusgovernment;
             return response;
         }