Fix xqueue auth settings

XQUEUE_INTERFACE needs to be defined even if XQUEUE is not enabled.

plugins/xqueue/tutorxqueue/patches/openedx-common-settings

@@ -1,4 +1,4 @@
-"XQUEUE_INTERFACE": {
+XQUEUE_INTERFACE = {
   "django_auth": {
     "username": "{{ XQUEUE_AUTH_USERNAME }}",
     "password": "{{ XQUEUE_AUTH_PASSWORD }}"

tutor/templates/apps/openedx/config/partials/auth.json

@@ -3,6 +3,10 @@
   "AWS_ACCESS_KEY_ID": "{{ OPENEDX_AWS_ACCESS_KEY }}",
   "AWS_SECRET_ACCESS_KEY": "{{ OPENEDX_AWS_SECRET_ACCESS_KEY }}",
   {{ patch("openedx-auth", separator=",\n", suffix=",")|indent(2) }}
+  "XQUEUE_INTERFACE": {
+      "django_auth": null,
+      "url": null
+  },
   "CONTENTSTORE": { 
     "ENGINE": "xmodule.contentstore.mongo.MongoContentStore",                       
     "DOC_STORE_CONFIG": {