Add cleanup functionality for container runner

[PGijsbers]

Moving TODOs from code to issue tracker (#172):

automlbenchmark/amlb/runners/container.py

Line 95 in 98bf554

# TODO: remove generated script? anything else?

Clean up for runner may potentially also include the stopped container (not sure if that already happens), or the image (though would not do that by default).

[PGijsbers]

Currently, cleanup is not implemented in any derived class, but is always called after a run.
I definitely would not want to remove the docker image after each run.
Perhaps the clean should only be called on --setup modes clean (#491) or force.
Then it could be something like:

    def cleanup(self):
        image = self._find_image()
        log.info(f"Cleaning up docker image {image}.")
        run_cmd(f"docker rmi -f {image}")
        log.info("Cleaning up Dockerfile")
        if os.path.exists(self._script):
            os.remove(self._script)