project/gateway2: Replaces Endpoints with EndpointSlice for Creating Upstream Endpoints

[danehans]

Description

Updates the gateway2 project to use EndpointSlice instead of Endpoints for creating upstream endpoints.

Fixes: https://github.com/solo-io/solo-projects/issues/6910

API changes

N/A

Code changes

The primary change is updating proxy_syncer.TransformUpstreamsBuilder() to transform an EndpointSlice into into a envoy_config_endpoint_v3.LbEndpoint instead of using an Endpoint.

CI changes

Removes skipping k8s GW API conformance tests.

Docs changes

N/A (internal change)

Context

Required for passing k8s gw api conformance tests.

Testing steps

Updates existing tests.

Notes for reviewers

N/A

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
  BOT NOTES:
  resolves https://github.com/solo-io/solo-projects/issues/6910

[solo-changelog-bot]

Issues linked to changelog:
https://github.com/solo-io/solo-projects/issues/6910

[danehans]

Converted to draft as I troubleshoot e2e failures.

[nfuden]

Likely there are some lookups that currently hard code to endpoints which may be causing the breaks

[yuval-k]

lgtm; left a note to myself