Add native support for Google Cloud Storage with GKE

[nick-stroud]

You can now configure a cluster and job to use a GCS bucket as a shared file system with GKE.

Note to reviewer:

• Each commit is self contained and can be reviewed independently
• First 3 commits are adding loosely related independent features that will be needed downstream
• Updated storage example job
  • to write to separate files as concurrent file operations was problematic at scale
  • to use both shared file systems

Tested: Deployed storage-gke.yaml blueprint and ran job.

Submission Checklist

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 Cloud HPC Toolkit Contribution guidelines #

[nick-stroud]

Will merge pending integration tests.