Add a sort parameter to Geo registries queries

This is so that admin users can sort the items in the Geo
dashboard better.
This commit adds:
- a new method `ordered_by` in the base registry;
- handling for a sort parameter in the finder class;
- the new sort argument in the registry resolver;
- associated tests.

Relates to: https://gitlab.com/gitlab-org/gitlab/-/issues/514998
EE: true
Changelog: added