add optional service argument to restart script

[mmguero]

The ./scripts/restart script (which is a symlink to control.py) currently just does a stop and then a start operation on the entire system.

It would be good if we modified control.py to be able to handle the -s/--service argument like we have for logs, and in that case only restart the one service. So:

• ./scripts/restartrestarts Malcolm
• ./scripts/restart -s api restarts just the API container

This came from this discussion.

[mmguero]

You can now specify one or more services with the -s/--service flag for the control.py script (e.g., start, stop, restart, logs) and it will apply only to those services. This is intended to be used while malcolm is already running, for example, to restart just a single service.

I tested making a change to a particular .env file in the config directory and then restarting the appropriate service, and verified that the restarted service does in fact get the new environment variables, as well.