Build Docker images with pre-installed PISCES

[mdshw5]

• Add a Dockerfile to define build process and entry point
• Set up gh-actions to build docker images and publish to Docker hub

[mdshw5]

@guma44 I'll update this issue with progress and issues building a docker image. We should discuss how to integrate the container in Cromwell. I find this in the Cromwell docs - is it a relevant starting point? baseCommand can be the pisces command, but I'm not sure about specifying inputs/outputs.