This reverts commit 20780a1eee.
* SECURITY: re-adds accidentally reverted commit:
03d26cd6: ensure embed_url contains valid http(s) uri
* when the merge commit e62a85cf was reverted, git chose the 2660c2e2 parent to land on
instead of the 03d26cd6 parent (which contains security fixes)
If the feature is enabled, staff members can construct a URL and publish a
topic for others to browse without the regular Discourse chrome.
This is useful if you want to use Discourse like a CMS and publish
topics as articles, which can then be embedded into other systems.
