Revert "fix: remove preview sites from allowed embedding pages (#25)" (#26)

This reverts commit 54507f4.

We revert this commit as the upstream change was merged in the master branch and is not to be backported to teak. Therefore, the current builds running on top of teak are failing.

Author: Danyal-Faheem

tutorjupyter/templates/jupyter/apps/jupyterhub_config.py

@@ -29,6 +29,8 @@
     "{% if ENABLE_HTTPS %}https{% else %}http{% endif %}://{{ LMS_HOST }}:8000",
     "{% if ENABLE_HTTPS %}https{% else %}http{% endif %}://{{ CMS_HOST }}",
     "{% if ENABLE_HTTPS %}https{% else %}http{% endif %}://{{ CMS_HOST }}:8001",
+    "{% if ENABLE_HTTPS %}https{% else %}http{% endif %}://{{ PREVIEW_LMS_HOST }}",
+    "{% if ENABLE_HTTPS %}https{% else %}http{% endif %}://{{ PREVIEW_LMS_HOST }}:8000",
 ]
 {% if MFE_HOST is defined %}
 frame_ancestors += [