[release-1.16] Add "cluster" type to subnet role validation

[k8s-infra-cherrypick-robot]

This is an automated cherry-pick of #5133

/assign mboersma

Add "cluster" type to subnet role validation

[willie-yao]

/lgtm
/approve

[k8s-ci-robot]

LGTM label has been added.

Git tree hash: 7eba49c609551d0de90fb0e6194eb711ac0dd517

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

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

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 51.20%. Comparing base (3edb4d4) to head (8a331c1).
Report is 3 commits behind head on release-1.16.

Additional details and impacted files

@@              Coverage Diff              @@
##           release-1.16    #5134   +/-   ##
=============================================
  Coverage         51.19%   51.20%           
=============================================
  Files               273      273           
  Lines             24626    24626           
=============================================
+ Hits              12607    12609    +2     
+ Misses            11230    11228    -2     
  Partials            789      789           

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