fix: added regex cluster name validation upon create

[mkarroqe]

What type of PR is this?
/kind bug

What this PR does / why we need it:
When creating a cluster with a . character in the cluster name, no warning is generated that it is an invalid regex character. This leads to the cluster stuck in a failed provisioning state when creating, and is unable to delete with the following error in the capz logs:

Invalid input: autorest/validation: validation failed: parameter=resourceName constraint=Pattern value="test.cluster.name" details: value doesn't match pattern ^[a-zA-Z0-9]$|^[a-zA-Z0-9][-_a-zA-Z0-9]{0,61}[a-zA-Z0-9]$

This PR adds validation for the cluster name in ValidateCreate() and extends existing unit tests.

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):
Fixes #3874

Special notes for your reviewer:

• cherry-pick candidate

TODOs:

• squashed commits
• includes documentation
• adds unit tests

Release note:

NONE

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[CecileRobertMichon]

@mkarroqe this PR is marked as draft, please mark it as ready for review / testing if it's ready

[mkarroqe]

Hi @CecileRobertMichon, thanks for the bump! I will pick this up again and try to have it in a reviewable state before the next CAPZ meeting.

[k8s-ci-robot]

PR needs rebase.

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[nawazkh]

Hey @mkarroqe , would love to discuss this over CAPZ meeting if you'd like! Feel free to mark it ready for review if it is ready!

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/lifecycle stale

[k8s-triage-robot]

The Kubernetes project currently lacks enough active contributors to adequately respond to all PRs.

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/lifecycle rotten