[release-1.19] Ensure all agent pool parameters are preserved in managed cluster creates

[k8s-infra-cherrypick-robot]

This is an automated cherry-pick of #5521

/assign nojnhuh

Fixed a bug causing an unnecessary update to an AKS agent pool after its managed cluster is created when certain fields are defined.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 52.61%. Comparing base (0172e1f) to head (1c994c5).
Report is 3 commits behind head on release-1.19.

Additional details and impacted files

@@               Coverage Diff                @@
##           release-1.19    #5524      +/-   ##
================================================
+ Coverage         52.57%   52.61%   +0.03%     
================================================
  Files               272      272              
  Lines             29470    29485      +15     
================================================
+ Hits              15495    15513      +18     
+ Misses            13167    13165       -2     
+ Partials            808      807       -1     

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[nojnhuh]

/kind bug
/lgtm
/approve

[k8s-ci-robot]

LGTM label has been added.

Git tree hash: c2d8de4ce620b7fc7ed9b9cb4dee57c67faa0d65

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: nojnhuh

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