Add support for Docker containerization

[devos50]

For our blockchain experiments, we are using Docker containers for resource isolation. It would be helpful if we can integrate Docker support in Gumby. When running an experiment locally or remotely, Gumby will start Docker containers and ensure that each instance runs within its own docker container. This would allow for more advanced experiment settings, e.g., emulating network latencies between different Docker containers.

See here for an example on how we run the Stellar blockchain within a Docker container.

Estimated time: 1 week