* Remove usage of deprecated testCompile configuration
* Replace testCompile usage by testImplementation
* Make testImplementation non transitive by default (as we did for testCompile)
* Update CONTRIBUTING about using testImplementation for test dependencies
* Fail on testCompile configuration usage
* Fix Snapshot Repository Corruption in Downgrade Scenarios (#50692)
This PR introduces test infrastructure for downgrading a cluster while interacting with a given repository.
It fixes the fact that repository metadata in the new format could be written while there's still older snapshots in the repository that require the old-format metadata to be restorable.