Enforce one target group per target group binding

[fawadkhaliq]

Issue

#2092

Description

Prevent creation of TargetGroupBinding if its already referenced by an existing TargetGroup

TargetGroupBinding has a one-to-one mapping with TargetGroup as per the data model, however, the controller does not enforce this behavior. This can lead to two TargetGroupBinding resources point to the same TargetGroup.

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 @fawadkhaliq. 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.

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[fawadkhaliq]

/assign @M00nF1sh

[codecov-commenter]

Codecov Report

Merging #2098 (eb3de77) into main (ed92ddf) will increase coverage by 0.00%.
The diff coverage is 45.45%.

@@           Coverage Diff           @@
##             main    #2098   +/-   ##
=======================================
  Coverage   49.23%   49.23%           
=======================================
  Files         130      130           
  Lines        7036     7046   +10     
=======================================
+ Hits         3464     3469    +5     
- Misses       3294     3297    +3     
- Partials      278      280    +2     

Impacted Files	Coverage Δ
webhooks/elbv2/targetgroupbinding_validator.go	79.59% <45.45%> (-7.59%)	⬇️

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[M00nF1sh]

/lgtm
/approve
🥂

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: fawadkhaliq, M00nF1sh

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