Bug 35218: Add unit tests for the counter registry API

Bug 35218: Add unit tests for the counter registry API

This patch adds two unit tests to cover the integration with the Counter Registry API in the Usage Statistics module. This is to prevent regressions caused either by changes to the Koha endpoint, or by changes to the Counter Registry API that might require changes in Koha to handle.

Test plan:
1) prove t/db_dependent/api/v1/erm_counter_registries.t
2) prove t/db_dependent/api/v1/erm_sushi_services.t

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>