Refactor code and enhance API documentation

- Converted `Question.cs` and `Search.cs` records to `record class` syntax for clarity.
- Organized API endpoints with tags and added new GET and DELETE endpoints in `Program.cs`, including OpenAPI documentation improvements.
- Removed commented-out code in `Program.cs` for cleaner codebase.
- Introduced `WithTags` for better API operation categorization in Swagger UI.
- Added a TODO comment in `ChatService.cs` for future improvement on chunk length check.
- Clarified `using` directives in `VectorSearchService.cs` with namespace aliasing to improve readability.
- Refactored document deletion in `VectorSearchService.cs` to use a private helper method and expanded service capabilities with a new `GetDocumentsAsync` method.
- Introduced a new `Document` model in the `Models` namespace to support document fetching functionality.
- Simplified `appsettings.json` by removing `MaxTokens` configuration for `ChatCompletion` and `Embedding` services.

SqlDatabaseVectorSearch/appsettings.json

@@ -6,14 +6,12 @@
         "ChatCompletion": {
             "Endpoint": "",
             "Deployment": "",
-            "ApiKey": "",
-            "MaxTokens": 32768
+            "ApiKey": ""
         },
         "Embedding": {
             "Endpoint": "",
             "Deployment": "",
-            "ApiKey": "",
-            "MaxTokens": 8191
+            "ApiKey": ""
         }
     },
     "AppSettings": {