Motivation

Some of the images that we're downloading to support our emulation are quite large, so I've been considering a way to show more info to the user about what's happening in the background.

This PR adds an additional argument, log_handler to the docker_client.pull(..) method, allowing service developers to inspect (or log) the exact output of the pull-command.

Example invocation

For example, to stream the logs to user (probably the most common usecase for this):

def some_action():
    ...
    def _process(line: str):
        LOG.debug(line)

    docker_client.pull_image("alpine", log_handler=_process)