Check for VM assigned identities without API calls

[nojnhuh]

What type of PR is this?
/kind cleanup

What this PR does / why we need it:

This PR removes the need to perform an extra API call for every reconciliation of every VM to determine whether the user assigned identities defined in an AzureMachine exist on the VM in Azure.

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):
Ref #2319

Special notes for your reviewer:

I did manually test that this still works as expected:

• Create a cluster where at least one AzureMachine defines a user-assigned identity (e.g. the control plane nodes in the default flavor)
• In the portal, remove the identity from the VM
• Wait for or trigger a reconciliation of the AzureMachine (e.g. kubectl label)
• Observe the VMIdentitiesReady condition appear on the AzureMachine with UserAssignedIdentityMissing

TODOs:

• squashed commits
• includes documentation
• adds unit tests
• cherry-pick candidate

Release note:

NONE

[nojnhuh]

We should make this available to scalability tests when we pin that to a release branch of CAPZ:

/cherry-pick release-1.20

[k8s-infra-cherrypick-robot]

@nojnhuh: once the present PR merges, I will cherry-pick it on top of release-1.20 in a new PR and assign it to you.

In response to this:

We should make this available to scalability tests when we pin that to a release branch of CAPZ:

/cherry-pick release-1.20

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.

[codecov]

Codecov Report

Attention: Patch coverage is 60.00000% with 4 lines in your changes missing coverage. Please review.

Project coverage is 52.81%. Comparing base (9ad724c) to head (5791ee2).
Report is 4 commits behind head on main.

Files with missing lines	Patch %	Lines
azure/converters/vm.go	0.00%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5780      +/-   ##
==========================================
- Coverage   52.82%   52.81%   -0.02%     
==========================================
  Files         279      279              
  Lines       29629    29602      -27     
==========================================
- Hits        15652    15634      -18     
+ Misses      13160    13154       -6     
+ Partials      817      814       -3     

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[willie-yao]

/lgtm
/approve

Good find! Not sure why I thought it was necessary to build a map of expected identities when we already had them lol

[k8s-ci-robot]

LGTM label has been added.

Git tree hash: 80d84ed26f6e4e7e1345e43e8b36488b4717cede

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: willie-yao

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Needs approval from an approver in each of these files:

• OWNERS [willie-yao]

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[k8s-infra-cherrypick-robot]

@nojnhuh: new pull request created: #5782

In response to this:

We should make this available to scalability tests when we pin that to a release branch of CAPZ:

/cherry-pick release-1.20

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.