[gw api] Add TG config logic to find and create user specified TG config.

[zac-nixon]

Description

Implements the logic to find and construct a TG config. The logic is simply finding the most relevant route specification in the list of potential route configurations and merging those values together with the TG config given in the default field.

Some notes about the logic:

• The tag and attribute merging logic is the same as the LB config tags & attributes. I have refactored the code to share the attribute & tagging logic.
• The route matching logic tries to find the best possible match. In order matching goes (kind + namespace + name) > (kind + namespace) > (kind). The route matching logic WILL NOT allow for a match when a namespace / name is specified and it does not match the route given.

Testing:

E2E tested, including the CRD changes. Added extensive unit tests.

Will add documentation a follow up PR that describes the merging behavior.

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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: zac-nixon

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[zac-nixon]

/retest

[shraddhabang]

/lgtm
/approved