Support of target annotations in gateway source

[solmonk]

Description

Supports external-dns.alpha.kubernetes.io/target annotation on Gateway Routes, so that the DNS record targets are configurable at Route level.

Expecting this to provide more flexibility on configuring DNS for different kinds of Gateway API implementations - please refer to #3749 for details on the issue.

Fixes #3749

Checklist

• Unit tests updated
• End user documentation updated

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: solmonk / name: Doyoon Kim (ff544d7, 851c4eb, 57d24f8, 9a030ad)

[k8s-ci-robot]

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[johngmyers]

Should we footnote to specify which annotations are supported on the Gateway and which on the various *Route resources? It looks like this PR only supports target on the *Route resources?

[johngmyers]

Would it be helpful to add test cases for the other *Route resource types?

[johngmyers]

Per my comments in #3749, I believe the target annotation should be consumed from the Gateway resource, not the various Route resources.

[k8s-ci-robot]

PR needs rebase.

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[johngmyers]

Implemented in #3452 (except the annotation is on the Gateway resource)
/close

[k8s-ci-robot]

@johngmyers: Closed this PR.

In response to this:

Implemented in #3452 (except the annotation is on the Gateway resource)
/close

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