Add a3u-gke-gcs blueprint

[samskillman]

In addition to the blueprint, which gives an opinionated way to mount buckets for training and checkpointing, I modified the gke-persistent-volume to be able to use the mount_options specified in network_storage. It previously just hardcoded implicit-dirs.

Submission Checklist

NOTE: Community submissions can take up to 2 weeks to be reviewed.

Please take the following actions before submitting this pull request.

• Fork your PR branch from the Toolkit "develop" branch (not main)
• Test all changes with pre-commit in a local branch #
• Confirm that "make tests" passes all tests
• Add or modify unit tests to cover code changes
• Ensure that unit test coverage remains above 80%
• Update all applicable documentation
• Follow Cluster Toolkit Contribution guidelines #

[ankitkinra]

LGTM but will allow storage experts to approve.

We should try to create an e2e integration test for this blueprint as soon as can.

[samskillman]

Rebased on top of current develop branch. I think this PR is ready for final review.