Verification of git reftables

Support reftables in Gitaly (gitlab-org&11653 - closed) tracks the work relating to the changes needed within gitaly to support the new reftables backend.

Part of this effort will likely require making some changes to some configuration to enable this feature. We'll want to create a new job to help verify these changes in gitlab-qa, and in the future potentially make this the default behaviour.

Similar to the praefect job, we will probably only need to run E2E tests that interact with gitaly, so we can scope this effort to a smaller subset of tests.