Fix RuntimeError: asyncio.run() cannot be called from a running event loop when calling mindmap endpoint. (#11880)

### What problem does this PR solve?

Fix RuntimeError when calling mindmap endpoint by converting
`gen_mindmap()` to async function and using `await` instead of
`asyncio.run()`.

### Type of change

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

---------

Co-authored-by: Kevin Hu <kevinhu.sh@gmail.com>

api/apps/conversation_app.py

@@ -435,7 +435,7 @@ async def mindmap():
     kb_ids.extend(req["kb_ids"])
     kb_ids = list(set(kb_ids))
 
-    mind_map = gen_mindmap(req["question"], kb_ids, search_app.get("tenant_id", current_user.id), search_config)
+    mind_map = await gen_mindmap(req["question"], kb_ids, search_app.get("tenant_id", current_user.id), search_config)
     if "error" in mind_map:
         return server_error_response(Exception(mind_map["error"]))
     return get_json_result(data=mind_map)