GitLab

can be set up using `pre-commit install`

This will push the images built by docker-images and docker-images-debug
target, if they exist.

This will result in make docker-images directly generating images with
appropriate tags.

Stops enqueuing messages but keeps synchronizing with the network

Includes setting a terminated flag and a call to detect this.

This will be used for orderly termination of simulators at different times
without blocking others.