promote HTTPRoute backend protocol from experimental to extended

[dprotaso]

What type of PR is this?
/kind gep
/area conformance

What this PR does / why we need it:
This promotes backend protocol selection as part of Gateway v1.2 release

Which issue(s) this PR fixes:
Part of #1911

Does this PR introduce a user-facing change?:

Backend Protocol Selection is no longer experimental and is now part of HTTPRoute Extended Conformance

[youngnick]

Is there any website documentation we need to update for this as well?

Aside from that, lgtm, I'll approve.

/approve

[dprotaso]

Sorry yeah - I need to drop this notice on this page https://gateway-api.sigs.k8s.io/guides/backend-protocol/

[dprotaso]

done

[robscott]

Thanks @dprotaso! This LGTM, but I think we need to have some kind of solution for #3115 before we accept docs updates for unreleased changes. I don't really have a great solution yet, but open to ideas.

[dprotaso]

Oh I didn't realize you don't have branches for the docs - should I rollback the docs change?

[robscott]

Oh I didn't realize you don't have branches for the docs - should I rollback the docs change?

Yeah unfortunately that's probably the best for now, but I really don't want to miss changing docs in the future. Hoping someone can help us figure out a better approach to docs versioning to make this less painful in the future.

[dprotaso]

Pulled the docs changes into a separate PR - #3120

[dprotaso]

I pulled out the docs changes into a separate PR. This change is ready to be merged.

[dprotaso]

weird verify took 2h

/retest

[robscott]

Thanks @dprotaso!

/lgtm
/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: dprotaso, robscott, youngnick

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