Refactor out references to Ambassador docker image

[rnorth]

We now use a socat container instead of the original ambassador container for exposing docker-compose ports.

The code (TestcontainersConfiguration) and docs still refer to the ambassador image, and this should be removed.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. If you believe this is a mistake, please reply to this comment to keep it open. If there isn't one already, a PR to fix or at least reproduce the problem in a test case will always help us get back on track to tackle this.