Update A3U blueprint to remove commit refs and remove hardcoded network names

[ighosh98]

This change ties variable names to dynamic deployment_variables instead of hard coded values. This ensures that collisions do not occur when users use cluster-toolkit to provision multiple clusters within the same project.

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• Fork your PR branch from the Toolkit "develop" branch (not main)
• Test all changes with pre-commit in a local branch #
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• 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 #

[ighosh98]

Additional validations regarding variable length would be evaluated in a follow up PR. Merging this one to unblock other developers