feat(chart): add priorityClassName for control plane pod

[starlightromero]

Proposed changes

Problem: The user is unable to set a priorityClassName for control plane pods. This could mean that the scheduler prioritizes other pods which rely on Nginx Gateway Fabric

Solution: Add a field to the Helm Chart to allow the user to set the priorityClassName for control plane pods.

Testing: Ran make lint-helm, make generate-helm-schema, and make generate-helm-docs

Checklist

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• 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.

- Allow setting priorityClassName on control plane pods

[nginx-bot]

Hi @starlightromero! Welcome to the project! 🎉

Thanks for opening this pull request!
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[github-actions]

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[starlightromero]

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