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_serializer.rb

@@ -39,4 +39,8 @@ class AdminUserSerializer < AdminUserListSerializer
   def registration_ip_address
     object.registration_ip_address.try(:to_s)
   end
+
+  def include_can_be_deleted?
+    true
+  end
 end