GAR integrations: Implement configuration test for the project integration

Description

We have been implementing the new project integration GoogleCloudPlatform::ArtifactRegistry without the configuration test Add GoogleCloudPlatform::ArtifactRegistry integ... (!141127 - merged)

In order to implement the integration test, the client class needs to be able to retrieve the repository details.

When the refactoring of the client class is done GAR Integration: Custom client class (#425147 - closed) we could go ahead and implement the configuration test.