refactor: Unify all json.(loads|dumps) usage to utils.json (#28702)

Co-authored-by: Eyal Ezer <eyal.ezer@ge.com>

superset/async_events/async_query_manager.py

@@ -14,7 +14,6 @@
 # KIND, either express or implied.  See the License for the
 # specific language governing permissions and limitations
 # under the License.
-import json
 import logging
 import uuid
 from typing import Any, Literal, Optional
@@ -23,6 +22,7 @@ import jwt
 import redis
 from flask import Flask, Request, request, Response, session
 
+from superset.utils import json
 from superset.utils.core import get_user_id
 
 logger = logging.getLogger(__name__)