container.stop and container.restart are missing the signal argument

[Kale-Ko]

Both stop and restart have supported customizing the signal that is sent to the container since api version v1.42 but it seems that it has not been added here. It would be very helpful if it could be added.

I would have a crack at it but I am not very familiar with writing unit tests. I saw that it is implemented for kill so it might not be too hard but I'm not sure.

[Kale-Ko]

I did go ahead and get it working but again I'm not sure how to do unit tests
main...Kale-Ko:docker-py:main

I tested it on a bash container with traps set up for SIGINT, SIGTERM, and SIGKILL and it gives the same results as docker stop -s {signal} {container} so I'd say it's working.