feat: Add Files API support with upload, list, get and delete operations

- Implement complete Files API compatible with Gemini API format
- Support resumable file uploads with chunked transfer (tested with 15MB video)
- Create file management service with database tracking
- Add file domain models and API request/response objects
- Implement file routes with proper authentication
- Use fixed API key for Files API requests (due to Google API restrictions)
- Support file state management (PROCESSING, ACTIVE, FAILED)
- Add scheduled task for automatic expired file cleanup
- Integrate seamlessly with existing key management and load balancing

app/log/logger.py

@@ -228,6 +228,10 @@ def get_request_log_logger():
     return Logger.setup_logger("request_log")
 
 
+def get_files_logger():
+    return Logger.setup_logger("files")
+
+
 def get_vertex_express_logger():
     return Logger.setup_logger("vertex_express")