[feat: gw api] Add finalizers for Rules CRD

[shraddhabang]

Description

Following the same strategy as of tgcfg and lbcfg to add the finalizers for rules CRD.
We will only check if the rules CRD is being referred by any L7 routes. If not, we remove the finalizers on the CRD.

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]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: shraddhabang

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• OWNERS [shraddhabang]

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[shuqz]

/lgtm /approved

[shuqz]

/lgtm