Add support for deployment labels to helm chart

[Butterneck]

Proposed changes

Problem: It's not possible to specify custom labels to be applied to the nginx gateway deployment

Solution: Add support for specifying custom labels to be applied on nginx gateway deployment

Testing: Run helm diff upgrade to test changes in rendered chart

Checklist

Before creating a PR, run through this checklist and mark each as complete.

• I have read the CONTRIBUTING doc
• I have added tests that prove my fix is effective or that my feature works
• I have checked that all unit tests pass after adding my changes
• I have updated necessary documentation
• I have rebased my branch onto main
• I will ensure my PR is targeting the main branch and pulling from my branch from my own fork

Release notes

If this PR introduces a change that affects users and needs to be mentioned in the release notes,
please add a brief note that summarizes the change.

NONE

[nginx-bot]

Hi @Butterneck! Welcome to the project! 🎉

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[github-actions]

✅ All required contributors have signed the F5 CLA for this PR. Thank you!
_{Posted by the CLA Assistant Lite bot.}

[Butterneck]

I have hereby read the F5 CLA and agree to its terms

[bjee19]

lgtm after change from @salonichf5 is addressed! 🚀

[salonichf5]

lgtm