Add support to disable cluster tag check during subnet auto-discovery

[oliviassss]

Issue

Description

Add a feature gate SubnetsClusterTagCheck to enable/disable the check for cluster tag kubernetes.io/cluster/${cluster-name} during subnet auto-discovery, with default value to true. When set to false, the subnets do not have to be tagged for current cluster.
This flag is to solve the user case that for EKS 1.19 and later versions, EKS stops adding the cluster tag kubernetes.io/cluster/{cluster-name} to subnets. For customer reusing the subnets for new 1.19 and later versions, the subnets will not be tagged for new clusters, so the subnets gets ignored during auto-discovery. In this case they can disable the cluster tag check so they do not need to tag the subnets for current cluster manually.

Tests

• Add unit tests to cover the change
• With SubnetsClusterTagCheck=true, created ALB and NLB with 2 subnets in the same AZ (1 tagged for current cluster, 1 tagged for other cluster), verified that the subnet tagged for current cluster got precedence.
• With SubnetsClusterTagCheck=false, created ALB and NLB with 2 subnets (both tagged for other clusters), verified the subnet got discovered by the order of subnet_id.
• With SubnetsClusterTagCheck=false, created ALB and NLB with 2 subnets (both contained no cluster tag at all), verified the subnet got discovered by the order of subnet_id.
• With SubnetsClusterTagCheck=false, created ALB and NLB with 2 subnets (1 tagged for current cluster, 1 tagged for other cluster), verified the subnet tagged for current cluster still got precedence.

Checklist

• Added tests that cover your change (if possible)
• Added/modified documentation as required (such as the README.md, or the docs directory)
• Manually tested
• Made sure the title of the PR is a good description that can go into the release notes

BONUS POINTS checklist: complete for good vibes and maybe prizes?! 🤯

• Backfilled missing tests for code in same general area 🎉
• Refactored something and made the world a better place 🌟

[k8s-ci-robot]

Hi @oliviassss. Thanks for your PR.

I'm waiting for a kubernetes-sigs member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

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[kishorj]

Need to so similar for NLB as well.

And some nit comments

[codecov-commenter]

Codecov Report

Merging #2635 (ee664e5) into main (cb4f483) will increase coverage by 0.03%.
The diff coverage is 76.92%.

@@            Coverage Diff             @@
##             main    #2635      +/-   ##
==========================================
+ Coverage   53.96%   53.99%   +0.03%     
==========================================
  Files         144      144              
  Lines        8202     8214      +12     
==========================================
+ Hits         4426     4435       +9     
- Misses       3458     3461       +3     
  Partials      318      318              

Impacted Files	Coverage Δ
pkg/config/feature_gates.go	0.00% <0.00%> (ø)
pkg/ingress/model_builder.go	64.21% <50.00%> (-0.15%)	⬇️
pkg/service/model_build_load_balancer.go	82.27% <50.00%> (-0.30%)	⬇️
pkg/ingress/model_build_load_balancer.go	63.95% <100.00%> (+0.14%)	⬆️
pkg/networking/subnet_resolver.go	92.77% <100.00%> (+0.16%)	⬆️
pkg/service/model_builder.go	88.04% <100.00%> (+0.26%)	⬆️

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[kishorj]

/ok-to-test

[kishorj]

/lgtm

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: kishorj, oliviassss

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