fix: lms installed apps without course_creators

Due course_creators is an studio app, when lms use `eox_nelp` it bring an error.
This avoid the following error ```RuntimeError: Model class cms.djangoapps.course_creators.models.CourseCreator doesn't declare an explicit app_label and isn't in an application in INSTALLED_APPS```.
So you have to add this one in the `INSTALLED_APPS`.

eox_nelp/settings/common.py

@@ -16,7 +16,7 @@
     'django_countries',
 )
 EOX_AUDIT_MODEL_APP = 'eox_audit_model.apps.EoxAuditModelConfig'
-
+COURSE_CREATOR_APP = 'cms.djangoapps.course_creators'
 
 def plugin_settings(settings):
     """
@@ -26,3 +26,5 @@ def plugin_settings(settings):
     settings.EOX_NELP_COURSE_CREATORS_BACKEND = 'eox_nelp.edxapp_wrapper.backends.course_creators_l_v1'
     if find_spec('eox_audit_model') and EOX_AUDIT_MODEL_APP not in settings.INSTALLED_APPS:
         settings.INSTALLED_APPS.append(EOX_AUDIT_MODEL_APP)
+    if COURSE_CREATOR_APP not in settings.INSTALLED_APPS:
+        settings.INSTALLED_APPS.append(COURSE_CREATOR_APP)