chore: bump Gateway API's Gateway from v1alpha2 to v1beta1

[pmalek]

What this PR does / why we need it:

This PR bump Gateway API Gateway resource from v1alpha2 to v1beta1.

Which issue this PR fixes:

Fixes #2899
Partially addresses #2887

Special notes for your reviewer:

This PR additionally introduces some type aliases in internal/controllers/gateway/types.go.

I was thinking to put that somewhere else where it could be reused by tests as well (at this moment it cannot due to it being in internal/ package next to test package) but I left it as is in current state.

I'm open for feedback w.r.t

PR Readiness Checklist:

Complete these before marking the PR as ready to review:

• the CHANGELOG.md release notes have been updated to reflect any significant (and particularly user-facing) changes introduced by this PR

[shaneutt]

From CI:

2022-09-06T18:17:23.3976511Z         	            	Internal error occurred: failed calling webhook "validations.kong.konghq.com": failed to call webhook: an error on the server ("unknown resource type to validate: gateway.networking.k8s.io/v1alpha2 gateways") has prevented the request from succeeding

[shaneutt]

Would seem we need another update to lock the k8s version in our CI:

failed to deploy addon metallb: resource mapping not found for name: "controller" namespace: "" from "https://raw.githubusercontent.com/metallb/metallb/v0.12.1/manifests/metallb.yaml": no matches for kind "PodSecurityPolicy" in version "policy/v1beta1"