Bump Gateway API Echo Image Tag

[danehans]

Do you have a suggestion for code improvement or tracking existing technical debt? Please describe.

solo-io#10232 adds initial support for TCPRoute. The echo image used by this PR for e2e TCPRoute testing is an older version, v20231214-v1.0.0-140-gf544a46e.

Describe the solution you'd like

Bump the image to v20240412-v1.0.0-394-g40c666fd used by the Gateway API v1.1.0 conformance tests.

Additional Context

The echo image is required to confirm responses by the correct backend for multi-backend TCPRoute testing.

[github-actions]

This issue has been marked as stale because of no activity in the last 180 days. It will be closed in the next 180 days unless it is tagged "no stalebot" or other activity occurs.

[timflannagan]

Looks like this is still relevant looking when searching for gcr.io/k8s-staging-gateway-api/echo-basic:v20231214-v1.0.0-140-gf544a46e references throughout the codebase. We should move the echo-basic to the common set of test app manifests while we're here.