[Epic] 2.1 Gateway API 1.4 Support

[timflannagan]

Placeholder epic for the upcoming 1.4 Gateway API release.

[timflannagan]

Have a branch locally that builds on top of gateway-api main and we're conformance with the upcoming 1.4 release.

The following changes needed to be made:

• The gw-api-crds Makefile target needed to use SSA kubectl apply. Likely related to the 1.34 bumps other projects have hit
• Several code changes related to the KAL linter being adopted upstream
• Update the GC status controller to set supportedFeatures in order to ensure we report conformance correctly going forward. Without it, we produced a barebones report for core functionality despite experimental CRDs being present locally. Additionally, updates to the conformance-related Makefile targets were needed here
  • Disabled the HTTPRouteCORS feature. IIRC, the issue was with the new CORSAllowCredentialsBehavior conformance test added in kubernetes-sigs/gateway-api@d28cd59, but needs more confirmation
  • Disabled all mesh core and experimental features. This is a no-op change as we don't support the GAMMA API for several classes
  • Disabled all the core/experimental BackendTLSPolicy features. This API is being promoted to v1 (or at least, there's an in-flight PR) and slatted for the 1.4 release. A lot more conformance tests were introduced that we aren't conformant with.
• Update cors related code to handle the changes made in Fix cors cel kubernetes-sigs/gateway-api#4032
• Update listener related code to handle the changes made in Move BackendTLS configuration to GatewayTLSConfig kubernetes-sigs/gateway-api#4009
• Additionally, I had to use a main branch version of the GIE dependency as Bumps k8s.io Deps to v0.34.0 kubernetes-sigs/gateway-api-inference-extension#1537 merged to main, but wasn't cherry picked to the release-1.0 branch. Without those changes, we cannot bump the gateway-api dependency.

TODO: Break this list down further.
TODO: Do we still need kubernetes-sigs/gateway-api#3823 or we all set given our TP API surface?

[timflannagan]

Bumping this from scratch likely became more difficult with the BTP promotion. There's some further coordination between other deps due to the 1.34 k8s.io changes before rc.1 was formally cut.

[timflannagan]

Needs istio/istio#57693 to merge as well.

[timflannagan]

Confirmed that supportedFeatures isn't strictly necessary for the bump. Here's the diff between main and a POC branch:

pushd .playground/issues/gw-api-1-4-bump && diff 1-3.yaml 1-4.yaml && popd
/work/kgateway/.playground/issues/gw-api-1-4-bump /work/kgateway ~
2c2
< date: "2025-09-24T17:20:26-04:00"
---
> date: "2025-09-24T17:31:49-04:00"
4c4
< gatewayAPIVersion: v1.3.0
---
> gatewayAPIVersion: v1.4.0-rc.1
25c25
<       Passed: 12
---
>       Passed: 13
32a33
>     - HTTPRouteNamedRouteRule
46a48
>     - HTTPRouteCORS
66c68
<       Passed: 12
---
>       Passed: 13
69a72,73
> succeededProvisionalTests:
> - HTTPRouteNamedRule

[danehans]

GIE v1.1 is expected ~Oct 20-23rd.