[WIP] Add ManagedGPUExperiencePreview nodepool and tests

[mboersma]

What type of PR is this?

/kind feature

What this PR does / why we need it:

Adds a GPU nodepool to the template introduced in #6128, enables the AKS ManagedGPUExperiencePreview, and runs Kuberay tests.

Which issue(s) this PR fixes:
Fixes #6131

Special notes for your reviewer:

We don't have much hope of getting quota for Standard_NC6s_v3 or similar SKUs in the short term, so this remains a work in progress.

TODOs:

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

Release note:

NONE

[k8s-ci-robot]

Skipping CI for Draft Pull Request.
If you want CI signal for your change, please convert it to an actual PR.
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[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 44.43%. Comparing base (13f39f2) to head (8dd8880).
⚠️ Report is 155 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #6164   +/-   ##
=======================================
  Coverage   44.43%   44.43%           
=======================================
  Files         280      280           
  Lines       25367    25367           
=======================================
  Hits        11272    11272           
  Misses      13283    13283           
  Partials      812      812           

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