[release-1.10] ignore AKS user-assigned ClientID/PrincipalID in diff

[nojnhuh]

What type of PR is this?
/kind bug

What this PR does / why we need it:

Manual cherry-pick of #3962:

This fixes a bug causing an endless reconciliation of AzureManagedControlPlane with spec.identity.type set to UserAssigned because of a continuous diff like this:

&armcontainerservice.ManagedCluster{
  	Location:         nil,
  	ExtendedLocation: nil,
  	Identity: &armcontainerservice.ManagedClusterIdentity{
  		DelegatedResources: nil,
  		Type:               &"UserAssigned",
  		UserAssignedIdentities: map[string]*armcontainerservice.ManagedServiceIdentityUserAssignedIdentitiesValue{
  			"/subscriptions/<sub>/resourcegroups/<group>/providers/Microsoft.ManagedIdentity/userAssignedIdentities/<name>": &{
- 				ClientID:    nil,
+ 				ClientID:    &"00000000-0000-0000-00000-00000000000",
- 				PrincipalID: nil,
+ 				PrincipalID: &"00000000-0000-0000-00000-00000000000",
  			},
  		},
  		PrincipalID: nil,
  		TenantID:    nil,
  	},
  	Properties: &{AutoScalerProfile: &{}, IdentityProfile: {"kubeletidentity": &{ResourceID: &"/subscriptions/<sub>/resourcegrou"...}}, KubernetesVersion: &"1.26.3", NetworkProfile: &{}, ...},
  	SKU:        &{Name: &"Base", Tier: &"Free"},
  	... // 5 identical fields
  }

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 #

Special notes for your reviewer:

• cherry-pick candidate

TODOs:

• squashed commits
• includes documentation
• adds unit tests

Release note:

Fixed a bug causing AzureManagedControlPlanes with `spec.identity.type` set to `UserAssigned` to needlessly reconcile constantly.

[Jont828]

/lgtm

[k8s-ci-robot]

LGTM label has been added.

Git tree hash: b5567b13055cc2329e0209885165f7e2e348e709

[CecileRobertMichon]

/lgtm
/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: CecileRobertMichon

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[codecov]

Codecov Report

Patch coverage: 100.00% and project coverage change: +0.01% 🎉

Comparison is base (f000d8d) 54.26% compared to head (bc99dde) 54.27%.
Report is 1 commits behind head on release-1.10.

Additional details and impacted files

@@               Coverage Diff                @@
##           release-1.10    #3963      +/-   ##
================================================
+ Coverage         54.26%   54.27%   +0.01%     
================================================
  Files               186      186              
  Lines             18855    18861       +6     
================================================
+ Hits              10231    10237       +6     
  Misses             8069     8069              
  Partials            555      555              

Files Changed	Coverage Δ
azure/services/managedclusters/spec.go	49.49% <100.00%> (+0.78%)	⬆️

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[nojnhuh]

Go modules 503:
/retest