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

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

tests/integration_tests/dashboards/dao_tests.py

@@ -16,13 +16,13 @@
 # under the License.
 # isort:skip_file
 import copy
-import json
 import time
 from unittest.mock import patch
 import pytest
 
 import tests.integration_tests.test_app  # pylint: disable=unused-import  # noqa: F401
 from superset import db, security_manager
+from superset.utils import json
 from superset.daos.dashboard import DashboardDAO
 from superset.models.dashboard import Dashboard
 from tests.integration_tests.base_tests import SupersetTestCase