[release-1.12] only consider spec in existing when reconciling ASO tags

[nojnhuh]

What type of PR is this?
/kind bug

What this PR does / why we need it:

Manual cherry-pick of #4531:

This PR offers an alternative fix to the issue addressed by #4149 which fixes the regression described by #4525. It eliminates CAPZ's use of ASO resources' status.tags from its reconciliation of tags in favor of only considering spec.tags which is easier to synchronize with CAPZ's extra bookkeeping in the last-applied-tags annotation.

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 where tags applied by Azure Policy were keeping CAPZ from reconciling ASO ResourceGroups and ManagedClusters

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (f82a7a8) 59.76% compared to head (de1098e) 59.75%.
Report is 3 commits behind head on release-1.12.

Additional details and impacted files

@@               Coverage Diff                @@
##           release-1.12    #4540      +/-   ##
================================================
- Coverage         59.76%   59.75%   -0.02%     
================================================
  Files               192      192              
  Lines             19316    19300      -16     
================================================
- Hits              11544    11532      -12     
+ Misses             7143     7139       -4     
  Partials            629      629              

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[nawazkh]

/lgtm

[k8s-ci-robot]

LGTM label has been added.

Git tree hash: 546facc894d5acd877ac8b134bb1816a6d2eb1a7

[mboersma]

/lgtm
/approve

[k8s-ci-robot]

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This pull-request has been approved by: mboersma

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