Updates gateway manifests for v1 InferencePool

[danehans]

Updates HTTPRoute manifests for all gateways other than GKE to use v1 InferencePool as a backendRef.

What type of PR is this?
/kind bug
/kind documentation

What this PR does / why we need it:

This PR is needed because a user cannot complete the quickstart guide for all gateways other than GKE. Additionally, we do not want to promote the alpha InferencePool API.

Which issue(s) this PR fixes:

Fixes #1602

Does this PR introduce a user-facing change?:

NONE

[k8s-ci-robot]

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This pull-request has been approved by: danehans

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[k8s-triage-robot]

Unknown CLA label state. Rechecking for CLA labels.

Send feedback to sig-contributor-experience at kubernetes/community.

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[nirrozenbaum]

would it be reasonable to update quickstart to use kgateway v2.1.0-dev until that release is finalized?
(and update to v2.1.0 after the release is cut)
ideally we want quickstart to work with all gateways by just following the steps.

/lgtm

[danehans]

@kfswain this PR should be backported to the release-1.0 branch and a v1.0.1 tag cut if #1604 is merged (versioned quickstart guide). Otherwise, users will continue to use the v1.0.0 manifests that contain bug #1602.