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)

plugins/discourse-narrative-bot/plugin.rb

@@ -55,6 +55,7 @@ after_initialize do
 
   module ::DiscourseNarrativeBot
     PLUGIN_NAME = "discourse-narrative-bot".freeze
+    BOT_USER_ID = -2
 
     class Engine < ::Rails::Engine
       engine_name PLUGIN_NAME
@@ -271,4 +272,9 @@ after_initialize do
       end
     end
   end
+
+  UserAvatar.register_custom_user_gravatar_email_hash(
+    DiscourseNarrativeBot::BOT_USER_ID,
+    "discobot@discourse.org"
+  )
 end