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

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

tests/integration_tests/sqllab_tests.py

@@ -17,7 +17,6 @@
 # isort:skip_file
 """Unit tests for Sql Lab"""
 
-import json
 from datetime import datetime
 from textwrap import dedent
 
@@ -45,6 +44,7 @@ from superset.sql_lab import (
 )
 from superset.sql_parse import CtasMethod
 from superset.utils.core import backend
+from superset.utils import json
 from superset.utils.json import datetime_to_epoch  # noqa: F401
 from superset.utils.database import get_example_database, get_main_database