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/db/services/dialog_service.py

@@ -13,7 +13,6 @@
 #  See the License for the specific language governing permissions and
 #  limitations under the License.
 #
-import asyncio
 import binascii
 import logging
 import re
@@ -887,7 +886,7 @@ async def async_ask(question, kb_ids, tenant_id, chat_llm_name=None, search_conf
     yield decorate_answer(answer)
 
 
-def gen_mindmap(question, kb_ids, tenant_id, search_config={}):
+async def gen_mindmap(question, kb_ids, tenant_id, search_config={}):
     meta_data_filter = search_config.get("meta_data_filter", {})
     doc_ids = search_config.get("doc_ids", [])
     rerank_id = search_config.get("rerank_id", "")
@@ -931,5 +930,5 @@ def gen_mindmap(question, kb_ids, tenant_id, search_config={}):
         rank_feature=label_question(question, kbs),
     )
     mindmap = MindMapExtractor(chat_mdl)
-    mind_map = asyncio.run(mindmap([c["content_with_weight"] for c in ranks["chunks"]]))
+    mind_map = await mindmap([c["content_with_weight"] for c in ranks["chunks"]])
     return mind_map.output