Test examples incrementally

[phlax]

currently we test all examples every time and do so outside of bazel

its not really possible (or at least not easy) to make the examples truly hermetic - mostly because they rely on system docker - if we were to switch to rules_docker they would still need to parse/translate the docker-compose instructions into docker rules

we can however make it almost hermetic - by using a bazel sourced docker-compose, using the required files as inputs and setting an action_env that set the container hash to use for envoy

potentially this can take a massive load off ci as well as making it faster, and also making it easier to (incrementally) test examples locally

[phlax]

one downside to using docker-compose from pypi is that it doesnt easily work on ARM (due to pynacl compile issues)

[phlax]

actually seems docker-compose release binaries - so that should resolve that issue i think

[github-actions[bot]]

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