[WIP] fix: stop endpoint events from rebuilding Gateway proxies

[chandler-solo]

Description

Prevent Pod and EndpointSlice events from triggering full Kubernetes Gateway proxy retranslation.

These resources already flow through the KRT endpoint pipeline, which updates the affected xDS endpoint resources. The legacy controller-runtime watches additionally called the global proxy Kick, causing every Gateway proxy to be rebuilt as often as once per second in event-heavy clusters.

Code changes

• Remove the legacy Pod and EndpointSlice controller registrations.
• Remove their reconcilers, whose only behavior was calling the global proxy Kick.
• Add a regression test proving that Service events still request proxy recomputation while Pod and EndpointSlice events do not.
• Add a changelog entry referencing solo-io/solo-projects#8013 with resolvesIssue: false.

Context

Investigation of solo-io/solo-projects#8013 found sustained CPU usage and heap growth dominated by Gateway API route translation, including buildProxy, translateGatewayHTTPRouteRule, setRouteAction, and RouteOptions.Clone.

Pod and EndpointSlice events currently enter two paths:

1. The KRT endpoint collections update endpoint resources in xDS.
2. The legacy controller-runtime reconcilers call Kick, causing all Gateway proxies and HTTPRoutes to be translated again.

The second path is redundant for endpoint-only changes and creates substantial CPU and allocation churn in clusters with frequent workload or endpoint updates.

This change addresses that unnecessary translation loop. It does not claim to fully resolve #8013; the independent cached Envoy snapshot retention addressed by #11309 has not yet landed.

Interesting decisions

The Pod and EndpointSlice controllers are removed instead of retained as no-op reconcilers. Their only behavior was calling Kick, and endpoint processing is already owned by the KRT collections.

Service, Secret, route, policy, ReferenceGrant, and Namespace watches remain unchanged because those resources can affect proxy translation or validation.

Testing steps

CGO_ENABLED=0 go test -count=1 \
  ./projects/gateway2/controller \
  ./projects/gateway2/krtcollections \
  ./projects/gateway2/proxy_syncer

The new envtest coverage uses a Service event as a positive control to verify that the Kick callback is active, then verifies that creating a Pod and EndpointSlice does not invoke it.

Notes for reviewers

Please verify that:

• Pod and EndpointSlice events no longer reach the global proxy recompute trigger.
• The KRT Pod and EndpointSlice collections remain unchanged and continue to update xDS endpoints.
• Resources that can affect proxy translation continue to call Kick.
• The changelog intentionally uses resolvesIssue: false.

Checklist:

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• Documentation changes are not required because this does not change an API or user workflow
• I have added tests that prove my fix is effective

# Description

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# Checklist:

- [ ] I have performed a self-review of my own code
- [ ] I have commented my code, particularly in hard-to-understand areas
- [ ] I have made corresponding changes to the documentation
- [ ] I have added tests that prove my fix is effective or that my feature works

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[solo-changelog-bot]

Issues linked to changelog:
https://github.com/solo-io/solo-projects/issues/8013

[github-actions]

Visit the preview URL for this PR (updated for commit 9554a80):

https://gloo-edge--pr11341-chandler-stop-endpoi-2gowlxo2.web.app

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