Container best practice is to use ENTRYPOINT rather than CMD

[bfjelds]

Our containers use CMD rather than ENTRYPOINT, but it seems that best practice is to use ENTRYPOINT:

https://docs.docker.com/develop/develop-images/dockerfile_best-practices/#entrypoint

We should change our dockerfiles according to best practices.

[DazWilkin]

Caveat: ./github/action/build-component-per-arch/main.js runs (bash) find in containers, assuming (which it shouldn't), that containers' (plural) entrypoint is a shell and that it's able to override some default command:

https://github.com/deislabs/akri/blob/fd2ed66c30c9fe4a7820a9b2feecfd3420da717e/.github/actions/build-component-per-arch/main.js#L96

A better practice (per the above) is for the container's primary function e.g. agent, controller etc. to be its entrypoint. Then, running containers is like running any other binary.

NOTE It's also preferable to not include superfluous functionality (e.g. bash) in a container whose function doesn't require bash; security, patching reasons etc.

Alternatives in this case:

1. Run the container and docker cp ${ID}:/path/to/known/location/container-images-legal-notice.md /somewhere/on/host
2. Retain bash or some other shell but make this a requirement for Akri developers so that you can --entrypoint=/bin/bash
3. Require container developers to host a small httpd that responds on any path by returning the legal notice

[kate-goldenring]

The Dockerfiles that should be changed live in our build directory