feat(instance): migrate placement-group resource to API v2

[Mia-Cross]

This PR is a duplicate from #6117, which was from a fork.
Review comments are on the original PR.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 95.43147% with 9 lines in your changes missing coverage. Please review.
✅ Project coverage is 50.77%. Comparing base (f969501) to head (1886049).
⚠️ Report is 1 commits behind head on main.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
...spaces/instance/v2alpha1/custom_placement_group.go	92.04%	7 Missing ⚠️
core/cobra_builder.go	77.77%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6132      +/-   ##
==========================================
- Coverage   50.78%   50.77%   -0.02%     
==========================================
  Files         359      361       +2     
  Lines       82302    82426     +124     
==========================================
+ Hits        41800    41848      +48     
- Misses      40502    40578      +76     

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