Course environment recipe as a Dockerfile

[tavareshugo]

We have added a Dockerfile to specify an image for the course (this is to make it easier to deploy this in the future).

However, the current Dockerfile is incomplete (missing R and Singularity). We will play around with this in the future, probably having a "base" image that can be used across courses, with things like mamba, nextflow, R, rstudio (server), singularity.

Then, we build things on top of that image with course-specific packages/environments.

This issue is here as a reminder for when we work on this again.