Make StaG-mwc Snakemake workflow standards compliant

[boulund]

https://snakemake.github.io/snakemake-workflow-catalog?rules=true

Major points to fix:

• [x] Move workflow into workflow subfolder
• [x] Create config folder and create config/README.md with instructions on how to fill out the config file
• [x] .snakemake-workflow-catalog.yaml in root

[boulund]

Possibly also add linting with snakemake --lint as a Github Action. Though we must ignore irrelevant warnings (e.g. /#.*/d in the metaphlan rules).

[boulund]

https://snakemake.readthedocs.io/en/stable/snakefiles/deployment.html#distribution-and-reproducibility

[boulund]

The main points have been handled and are soon merged to develop for the upcoming 0.6 release https://github.com/ctmrbio/stag-mwc/pull/205