Revert "Revert "Merge branch 'master' of https://github.com/discourse/discourse""

This reverts commit 20780a1eeed56b321daf18ee6bbfe681a51d1bf4.

* 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)

spec/lib/bookmark_reminder_notification_handler_spec.rb

@@ -8,7 +8,7 @@ RSpec.describe BookmarkReminderNotificationHandler do
   fab!(:user) { Fabricate(:user) }
 
   before do
-    Discourse.redis.flushall
+    Discourse.redis.flushdb
   end
 
   describe "#send_notification" do