add support for targetgroupbinding cross-account AZ aware registration

[cqi1217]

Issue

#4831

Description

Cross-account TargetGroupBindings always register IP targets with AvailabilityZone: "all".
Because every zonal load balancer node can then forward to every target, disabling NLB
cross-zone load balancing has no effect and inter-AZ data transfer is unavoidable for
anyone using the hub/spoke pattern (NLB + target groups in a central account, workloads
in spoke accounts).

The "all" value is hardcoded for cross-account in prepareRegistrationCall, which gated
the pod-AZ path on usePodAZ && !usingCrossAccount.

This PR adds an opt-in spec.registerTargetsWithPodAvailabilityZone field that registers
each target with the AZ of the node its pod runs on.

Why the AZ name can't be used directly

AZ names are randomized per account — us-west-2a in the cluster's account is usually a
different physical zone than us-west-2a in the target group owner's account. AZ IDs
(e.g. usw2-az1) are stable across accounts, so the new AZIDTranslator resolves:

pod's zone name --(CO credentials)--> zone ID --(assumed role)--> TGO zone name

Key changes

• pkg/networking/az_id_translator.go (new) — AZIDTranslator.TranslateAZName()
  performs the two-hop lookup above. Results are cached for 60 minutes to avoid throttling
  DescribeAvailabilityZones on every reconcile. The cache key is
  {scope, lookup} where scope is the assumed role ARN (empty for the cluster's own
  account), so zone names from different accounts can never collide — an important detail
  given that the same name means different things per account.

• Assumed-role EC2 client — the translator's second lookup has to run with TGO
  credentials, so EC2 gained AssumeRole() and defaultCloud gained GetAssumedRoleEC2()
  plus an assumeRoleEc2Cache, mirroring the existing GetAssumedRoleELBV2() path. The STS
  assume-role + config construction shared by both is factored out into
  generateAssumedRoleConfig(). All ec2Client methods now route through a getClient()
  helper so a statically-provided assumed-role client is honored.

• pkg/targetgroupbinding/resource_manager.go — the gate becomes
  (usePodAZ && !usingCrossAccount) || usePodAZForCrossAccount. The new
  resolveTargetAvailabilityZone() looks up the pod AZ and translates it when cross-account.

• Webhook validation — rejects the field without iamRoleArnToAssume.

• API/CRD — field added to both v1beta1 and v1alpha1. Since the CRD has no
  conversion webhook (strategy: None), a field present in only one served version would be
  pruned when the object is read or written through the other, so both need it. This matches
  how the existing iamRoleArnToAssume / assumeRoleExternalId fields are defined.

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 🌟

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: cqi1217 / name: cqi1217 (cab5bca)

[kubernetes-prow]

Welcome @cqi1217!

It looks like this is your first PR to kubernetes-sigs/aws-load-balancer-controller 🎉. Please refer to our pull request process documentation to help your PR have a smooth ride to approval.

You will be prompted by a bot to use commands during the review process. Do not be afraid to follow the prompts! It is okay to experiment. Here is the bot commands documentation.

You can also check if kubernetes-sigs/aws-load-balancer-controller has its own contribution guidelines.

You may want to refer to our testing guide if you run into trouble with your tests not passing.

If you are having difficulty getting your pull request seen, please follow the recommended escalation practices. Also, for tips and tricks in the contribution process you may want to read the Kubernetes contributor cheat sheet. We want to make sure your contribution gets all the attention it needs!

Thank you, and welcome to Kubernetes. 😃

[kubernetes-prow]

Hi @cqi1217. 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.

Once the patch is verified, the new status will be reflected by the ok-to-test label.

I understand the commands that are listed here.

Details

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes-sigs/prow repository.

[kubernetes-prow]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: cqi1217
Once this PR has been reviewed and has the lgtm label, please assign shraddhabang for approval. For more information see the Code Review Process.

The full list of commands accepted by this bot can be found here.

Details

Needs approval from an approver in each of these files:

• OWNERS

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[cqi1217]

hi @wweiwei-li @shraddhabang can you review the code? thank you