Improve storage engine (#4341)

### What problem does this PR solve?

- Bring `STORAGE_IMPL` back in `rag/svr/cache_file_svr.py`
- Simplify storage connection when working with AWS S3

### Type of change

- [x] Refactoring

rag/svr/cache_file_svr.py

@@ -19,7 +19,7 @@ import traceback
 
 from api.db.db_models import close_connection
 from api.db.services.task_service import TaskService
-from rag.utils.minio_conn import MINIOs
+from rag.utils.storage_factory import STORAGE_IMPL
 from rag.utils.redis_conn import REDIS_CONN
 
 
@@ -44,7 +44,7 @@ def main():
                     key = "{}/{}".format(kb_id, loc)
                     if REDIS_CONN.exist(key):
                         continue
-                    file_bin = MINIOs.get(kb_id, loc)
+                    file_bin = STORAGE_IMPL.get(kb_id, loc)
                     REDIS_CONN.transaction(key, file_bin, 12 * 60)
                     logging.info("CACHE: {}".format(loc))
                 except Exception as e: