hook: Send repository relative path to access check

During the execution of the prereceive hook, Gitaly makes a call to the /allowed endpoint on the GitLab API. This is done to perform access checks which determine if the incoming objects, which are initially quarantined, should be accepted into the repository.

As part of the access checks, the quarantined objects may need to be visible to GitLab. To accommodate this, both GIT_OBJECT_DIRECTORY and GIT_ALTERNATE_OBJECT_DIRECTORIES, which contain the main and quarantined object directories, are provided to the access checks. This enables quarantined objects in a repository to be visible during downstream Gitaly calls.

With the new transaction management in Gitaly, this approach needs to be adapted to support access checks on the transaction snapshot instead of the original repository. To help facilitate this, the repository relative path is now provided to the GitLab /allowed endpoint. Future changes to the GitLab API are required to use this additional parameter to perform appropriate access checks.