[Bug]: Dockerfile does not include a CMD command

Summary of Problem

Our Dockerfile for Chapel does not include a CMD nor an ENTRYPOINT. From the Docker docs: https://docs.docker.com/reference/dockerfile/#understand-how-cmd-and-entrypoint-interact

Dockerfile should specify at least one of CMD or ENTRYPOINT commands. No CMD and no ENTRYPOINT is an error, and is not allowed.

How does our Docker image build successfully then? We inherit the default CMD command from the debian 11 image which we use as our base.

We should not rely on this behavior from debian, and instead should add a line to our Dockerfile that says

CMD ["/bin/bash"]