Fixes for the rename reserved paths helpers

This makes sure only the routes that belong to a certain namespace get renamed, instead of the ones that start with the same name.

Closes #32528 (closed)

And it makes sure that users get a new username when their namespace changes: #32526 (closed)

lib/gitlab/database/rename_reserved_paths_migration/v1/migration_classes.rb

@@ -48,6 +48,14 @@ module Gitlab
             def self.name
               'Namespace'
             end
+
+            def kind
+              type == 'Group' ? 'group' : 'user'
+            end
+          end
+
+          class User < ActiveRecord::Base
+            self.table_name = 'users'
           end
           class Route < ActiveRecord::Base