FEATURE: set notification levels when added to a group (#10378)

* FEATURE: set notification levels when added to a group

This feature allows admins and group owners to define default
category and tag tracking levels that will be applied to user
preferences automatically at the time when users are added to the
group. Users are free to change those preferences afterwards.
When removed from a group, the user's notification preferences aren't
changed.

app/controllers/groups_controller.rb

@@ -604,6 +604,13 @@ class GroupsController < ApplicationController
         default_params
       end
 
+    if !automatic || current_user.admin
+      [:muted, :tracking, :watching, :watching_first_post].each do |level|
+        permitted_params << { "#{level}_category_ids" => [] }
+        permitted_params << { "#{level}_tags" => [] }
+      end
+    end
+
     params.require(:group).permit(*permitted_params)
   end