FEATURE: Add bulk destroy to admin users list (#29744)

This commit introduces a new feature that allows staff to bulk select and delete users directly from the users list at `/admin/users/list`. The main use-case for this feature is make deleting spammers easier when a site is under a large spam attack.

Internal topic: t/140321.

app/serializers/admin_user_list_serializer.rb

@@ -24,7 +24,8 @@ class AdminUserListSerializer < BasicUserSerializer
              :silenced_till,
              :time_read,
              :staged,
-             :second_factor_enabled
+             :second_factor_enabled,
+             :can_be_deleted
 
   %i[days_visited posts_read_count topics_entered post_count].each do |sym|
     attributes sym
@@ -111,4 +112,12 @@ class AdminUserListSerializer < BasicUserSerializer
   def second_factor_enabled
     true
   end
+
+  def can_be_deleted
+    scope.can_delete_user?(object)
+  end
+
+  def include_can_be_deleted?
+    @options[:include_can_be_deleted]
+  end
 end