[release-1.10] Set correct fqdn on private cluster

[mihaiandreiratoiu]

What type of PR is this?
Adapted from #4225
/kind bug

What this PR does / why we need it:
On private cluster with the managedcontrolplane

• EnablePrivateCluster: true
• EnablePrivateClusterPublicFQDN: false
  The fqdn property is not available. The cluster defaults to the privateFQDN
  The Cluster resource remains in provisioning state due to the capz error

spec.controlPlaneEndpoint.host: Required value" "AzureManagedCluster"

Special notes for your reviewer:

• cherry-pick candidate
• to cherry-pick into release-1.11

TODOs:

• squashed commits
• includes documentation
• adds unit tests

Release note:

 Fix: Set correct host on private cluster with public fqdn disabled

[k8s-ci-robot]

Hi @mihaiandreiratoiu. Thanks for your PR.

I'm waiting for a kubernetes-sigs member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

Once the patch is verified, the new status will be reflected by the ok-to-test label.

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[nojnhuh]

/ok-to-test

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (f47fd94) 54.36% compared to head (b18aaf7) 54.38%.
Report is 1 commits behind head on release-1.10.

Additional details and impacted files

@@               Coverage Diff                @@
##           release-1.10    #4241      +/-   ##
================================================
+ Coverage         54.36%   54.38%   +0.01%     
================================================
  Files               186      186              
  Lines             18898    18906       +8     
================================================
+ Hits              10274    10282       +8     
  Misses             8069     8069              
  Partials            555      555              

Files	Coverage Δ
azure/services/managedclusters/managedclusters.go	80.28% <100.00%> (+2.50%)	⬆️

☔ View full report in Codecov by Sentry.
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[nojnhuh]

/lgtm
/approve

[k8s-ci-robot]

LGTM label has been added.

Git tree hash: 8a2a684e693be87ff2f08e3c26a75aa3f8945b89

[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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[mboersma]

/lgtm++

Thanks @mihaiandreiratoiu!

[nojnhuh]

/retest