Allow limiting the number of nodegroups created in parallel

[cPu1]

Description

Adds support for a new option nodegroup-parallelism to create cluster and create nodegroup that allows limiting the number of nodegroups created in parallel. Adding integration tests for this change would require more time so we may revisit it later.

Checklist

• Added tests that cover your change (if possible)
• Added/modified documentation as required (such as the README.md, or the userdocs directory)
• Manually tested
• Made sure the title of the PR is a good description that can go into the release notes
• (Core team) Added labels for change area (e.g. area/nodegroup) and kind (e.g. kind/improvement)

BONUS POINTS checklist: complete for good vibes and maybe prizes?! 🤯

• Backfilled missing tests for code in same general area 🎉
• Refactored something and made the world a better place 🌟