Refactor project structure and add new features

Restructured project files across all layers:
- Removed `Controllers` folder reference from `DocumentOperator.API.csproj`.
- Added folder structure to `DocumentOperator.Application`, `DocumentOperator.Domain`, and `DocumentOperator.Infrastructure` projects for better organization.

Introduced new API configurations and middleware:
- Added `SerilogConfiguration` and `SwaggerConfiguration` classes.
- Added `ExceptionHandlingMiddleware`, `RequestLoggingMiddleware`, and `TenantResolutionMiddleware`.

Implemented new document processing feature:
- Added `ProcessDocumentCommand`, `ProcessDocumentHandler`, and `ProcessDocumentValidator` classes in the application layer.

DocumentOperator.Domain/DocumentOperator.Domain.csproj

@@ -6,4 +6,12 @@
     <Nullable>enable</Nullable>
   </PropertyGroup>
 
+  <ItemGroup>
+    <Folder Include="Common\Exceptions\" />
+    <Folder Include="Common\Results\" />
+    <Folder Include="Constants\" />
+    <Folder Include="Models\Enums\" />
+    <Folder Include="Models\ValueObjects\" />
+  </ItemGroup>
+
 </Project>