Update config structure and enhance file handling

Renamed API_V1_STR to API_VERSION_STR for consistency. Introduced 'UPLOAD_FOLDER' and ensured its creation, added logging for the data directory path, and implemented allowed image content type validation. Adjusted related references in `main.py`.

backend/app/main.py

@@ -17,7 +17,7 @@ logger.info(f"Starting app!!!")
 app = FastAPI(
     title=settings.PROJECT_NAME,
     version=settings.VERSION,
-    openapi_url=f"{settings.API_V1_STR}/openapi.json"
+    openapi_url=f"{settings.API_VERSION_STR}/openapi.json"
 )
 
 # Set up CORS middleware
@@ -46,5 +46,5 @@ async def root():
     """
 
 
-app.include_router(api_router, prefix=settings.API_V1_STR)
+app.include_router(api_router, prefix=settings.API_VERSION_STR)
 app.mount("/files", StaticFiles(directory=settings.DATA_FILES_DIR), name="static")