feat: Implement file upload and folder creation features by GO (#13903)

### What problem does this PR solve?

feat: Implement file upload and folder creation features

- Add file upload route in router.go
- Add file operation methods in dao/file.go
- Add util/file.go for file type detection and filename handling
- Implement file upload and folder creation endpoints in handler/file.go
- Implement file upload and folder creation logic in service/file.go
- Modify response message format in memory.go
- Add document count method in dao/document.go

### Type of change

- [x] New Feature (non-breaking change which adds functionality)

internal/router/router.go

@@ -189,6 +189,12 @@ func (r *Router) Setup(engine *gin.Engine) {
 			// 	message.GET("", r.memoryHandler.GetMessages)
 			// 	message.GET("/:memory_id/:message_id/content", r.memoryHandler.GetMessageContent)
 			// }
+
+			file := v1.Group("/files")
+			{
+				file.POST("", r.fileHandler.UploadFile)
+			}
+
 			// provider pool route group
 			provider := v1.Group("/providers")
 			{