Improve file management (#10577)

### What problem does this PR solve?

Improve file management. #10287.

Passed tests:

1. Create folder `A` and `B`.
2. Upload a file inside `A`, called `file`.
3. Create a KB, called `K`.
3. Link `file` to `K`.
4. Parse `file` inside of `K`. (OK)
5. Move `file` from `A` to `B`.
6. Parse `file` inside of `K`. (OK)
7. Move `file` from `B` to `A`.
8. Parse `file` inside of `K`. (OK)
9. Move entire folder `A` into `B`. (B -> A -> file)
10. Parse `file` inside of `K`. (OK)
11. Delete folder `B`.
12. All clear. (There is no document inside of `K`)

### Type of change

- [x] Bug Fix (non-breaking change which fixes an issue)

api/db/services/file_service.py

@@ -476,6 +476,16 @@ class FileService(CommonService):
 
         return err, files
 
+    @classmethod
+    @DB.connection_context()
+    def list_all_files_by_parent_id(cls, parent_id):
+        try:
+            files = cls.model.select().where((cls.model.parent_id == parent_id) & (cls.model.id != parent_id))
+            return list(files)
+        except Exception:
+            logging.exception("list_by_parent_id failed")
+            raise RuntimeError("Database error (list_by_parent_id)!")
+
     @staticmethod
     def parse_docs(file_objs, user_id):
         exe = ThreadPoolExecutor(max_workers=12)