Add dockerfile

[Edgar-21]

Heavily inspired by a dockerfile shared by Shimwell here https://forum.coreform.com/t/trelis-in-docker/442/2.

Uses the miniconda docker image as the base (Debian Bullseye), found here https://hub.docker.com/r/continuumio/miniconda3. To use cubit, the image can be run interactively, and the license file copied to the appropriate location. Cubit works in terminal with the --no-graphics option and can be imported into python.

I expect it will need a couple additions for this to work with Github actions. I'll start looking at that documentation in the next few days, in the meantime wanted to get this posted to get some eyes on it sooner rather than later

fixes #57

[Edgar-21]

perhaps this goes without saying but this will also need the parastell dependencies added, I was thinking about doing that with conda/mamba since that is how our install instructions are written

[gonuke]

Thanks @Edgar-21 - we might want to consolidate the dependencies

[gonuke]

We need to add the environment file here too.

[Edgar-21]

This has a conda environment named parastell_env. After adding the license and activating the environment, ExampleScript.py from the main branch will run to completion and generate the expected outputs, at least when I run it

[gonuke]

I think this works for me. I have a few convenience suggestions.

[gonuke]

Thanks @Edgar-21 - this works for me