Update spack openfoam example to Slurm V6

[harshthakkar01]

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 #

[cboneti]

Please also fix the documentation:

1. point to our fork of Slurm-GCP.
2. the spack cache comment is outdated now, are we using the GCP cache by default? what is the completion time?
3. Cluster deployment: you changed the deployment name, therefore, you have to change the deployment steps. The connection to the controller will also be affected since the cluster name, with v6, will likely be different. Same goes with the login node.

Addressed.