exposing constants to be backwards compatible (#24765)

* exposing constants to be backwards compatible

openedx/core/djangoapps/plugins/constants.py

+"""
+Constants used by django app plugins
+"""
+
+# expose constants from edx-django-utils so plugins using these continue to work
+from edx_django_utils.plugins import (
+    PluginSettings,  # pylint: disable=unused-import
+    PluginURLs,  # pylint: disable=unused-import
+    PluginSignals,  # pylint: disable=unused-import
+    PluginContexts,  # pylint: disable=unused-import
+)
+
 
 class ProjectType():
     """