Docker integration

[maarten-ic]

Add integration with docker, such that muscle_manager can directly launch components in a docker container.

Example:

implementations:
  component_in_docker:
    docker_image: my_own_docker_image
    executable: /path/in/docker/image/to/my/executable

Main benefit compared specifying docker as executable and providing the correct arguments:

• muscle_manager can arrange Docker port forwarding, such that this component can talk to the muscle_manager and peer instances.
• muscle_manager can transparently set the correct environment variables that are required for the program running inside Docker

[LourensVeen]

Should this be Docker, or Singularity, or something else, or all of them? Docker isn't widely supported on HPC because of security issues, Singularity is but isn't used much outside of HPC, and there may still be other things in use. At least if we start with Docker it may be good to use docker_image instead of image to ensure we can extend in the future, and to make it clear what's expected.

[maarten-ic]

That is a good question! Docker integration came up in a workshop last week, I don't know about Singularity or other containerization.

I've updated the issue description to change image -> docker_image.