Set cluster name label for pre-existing kubeconfig

[willie-yao]

What type of PR is this?
/kind bug

What this PR does / why we need it:
This PR adds a fix for clusters upgrading from before CAPI v1.5 to a newer version. v1.5 introduced a new requirement for the ClusterNameLabel to be added to kubeconfig secrets: https://cluster-api.sigs.k8s.io/developer/providers/migrations/v1.4-to-v1.5#other

CAPZ handles this for newly created kubeconfigs, but not pre-existing ones. This PR handles that case.

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 #4738

Special notes for your reviewer:

• cherry-pick candidate

TODOs:

• squashed commits
• includes documentation
• adds unit tests

Release note:

Set cluster name label for pre-existing kubeconfig

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 4 lines in your changes are missing coverage. Please review.

Project coverage is 62.00%. Comparing base (abba169) to head (d4fda95).
Report is 81 commits behind head on main.

Files	Patch %	Lines
controllers/azuremanagedcontrolplane_reconciler.go	0.00%	3 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4833      +/-   ##
==========================================
- Coverage   62.62%   62.00%   -0.62%     
==========================================
  Files         198      201       +3     
  Lines       16285    16862     +577     
==========================================
+ Hits        10198    10455     +257     
- Misses       5341     5624     +283     
- Partials      746      783      +37     

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

[mboersma]

/lgtm

It would be nice to cover this with a unit test, but I see there aren't any around Reconcile or reconcileKubeconfig yet. So that's probably too much to ask for this bug fix.

Thanks for fixing this @willie-yao!

[k8s-ci-robot]

LGTM label has been added.

Git tree hash: f4336d27f3e9b7e28ed8afe42711456917398031

[mboersma]

/assign @nojnhuh

[nojnhuh]

/lgtm
/approve

Thanks Willie!

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: nojnhuh

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• OWNERS [nojnhuh]

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[willie-yao]

/cherry-pick release-1.14

[willie-yao]

/cherry-pick release-1.13

[k8s-infra-cherrypick-robot]

@willie-yao: new pull request created: #4846

In response to this:

/cherry-pick release-1.14

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes-sigs/prow repository.

[k8s-infra-cherrypick-robot]

@willie-yao: new pull request created: #4847

In response to this:

/cherry-pick release-1.13

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes-sigs/prow repository.

[willie-yao]

/cherry-pick release-1.15

[k8s-infra-cherrypick-robot]

@willie-yao: new pull request created: #4848

In response to this:

/cherry-pick release-1.15

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes-sigs/prow repository.