Add support for additional praefect tests

Allows tests to be run that require Praefect to be configured as a repository storage.

The Praefect scenario has Praefect configured as the default storage, so it can run such tests. They can also run on Staging or other environments, provided QA_PRAEFECT_REPOSITORY_STORAGE is set appropriately.

Part of gitlab-org/quality/testcases#276 (closed)

Depends on gitlab!27295 (merged). Both MRs should be merged and released together.