Add "cluster" type to subnet role validation

[mboersma]

What type of PR is this?

/kind bug

What this PR does / why we need it:

Adds "cluster" to the valid kubebuilder types for a subnet role, as documented. Apparently we had added "all" instead.

cluster-api-provider-azure/api/v1beta1/types.go

Lines 744 to 745 in 3770549

	// SubnetCluster defines a role that can be used for both Kubernetes control plane node and Kubernetes workload node.
	SubnetCluster = SubnetRole(Cluster)

Which issue(s) this PR fixes:
Fixes #5130

Special notes for your reviewer:

• cherry-pick candidate

TODOs:

• squashed commits
• includes documentation
• adds unit tests

Release note:

Add "cluster" type to subnet role validation

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 51.25%. Comparing base (3770549) to head (76ce65f).
Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #5133   +/-   ##
=======================================
  Coverage   51.25%   51.25%           
=======================================
  Files         273      273           
  Lines       24651    24651           
=======================================
+ Hits        12634    12636    +2     
+ Misses      11231    11229    -2     
  Partials      786      786           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[mboersma]

/cc @nojnhuh @willie-yao

[nojnhuh]

I wonder if this is something we'd technically have to call a breaking change if all is no longer valid when it was before. Maybe we have more wiggle room here if all was never functional anyway?

[mboersma]

I thought of that--someone may have read the source code to figure out that "all" would pass validation. But AFAICT there is no code that handles SubnetRole("all"), no tests around that, and no constant defined for it, so it was not intentionally functional and didn't act as SubnetCluster is intended to.

[nojnhuh]

FYI @LochanRn

[nojnhuh]

/lgtm
/approve

[k8s-ci-robot]

LGTM label has been added.

Git tree hash: fe0a3c964423805dd3b51b9fdc4f409070654935

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: nojnhuh

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[mboersma]

/cherry-pick release-1.16

[k8s-infra-cherrypick-robot]

@mboersma: new pull request created: #5134

In response to this:

/cherry-pick release-1.16

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