Add code changes to improve how additional networks are passed in A3 ultra blueprint

[parulbajaj01]

Additional networks are not configured by the user. Moreover, readability is not good. Made changes in gke-a3-ultragpu blueprint to improve code readability. Made changes in gke-cluster, gke-nodepool and vpc modules to pass the correct outputs according to the changes.

Submission Checklist

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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 #

[tpdownes]

Adding do not merge label until we resolve internal discussions