FEATURE: Make allow_uploaded_avatars accept TL (#14091)

This gives admins more control over who can upload custom profile
pictures.

spec/components/composer_messages_finder_spec.rb

@@ -144,7 +144,7 @@ describe ComposerMessagesFinder do
     end
 
     it "doesn't notify users if 'allow_uploaded_avatars' setting is disabled" do
-      SiteSetting.allow_uploaded_avatars = false
+      SiteSetting.allow_uploaded_avatars = 'disabled'
       expect(finder.check_avatar_notification).to be_blank
     end
   end