Fixes #12644, #12643 - Correctly authorize in lookup key index

There was a problem with the authorizer for lookup key indices that led
to problems with sorting and searching.
Because `#includes` lazy loads the included relation, and the authorizer
didn't need the relation, it didn't load the puppetclass or the
lookup_value table. However, the search_for scope added an order_by or a
where condition to @lookup_keys, which caused the authorizer collection
to create an invalid query.