Create a "mulled biocontainers" to bio.tools metadata sync

[hmenager]

The current CI process only sends metadata about containers generated from Dockerfiles. We would need to do the same for all containers generated with mulled, so that the research-software-ecosystem/content repository has a file for each available mulled biocontainers as well.
Happy to take any suggestion on this.

[hmenager]

Would probably adopt the same strategy and results as the one suggested for dockerfile biocontainers in #12

[hmenager]

from discussion with @bgruening this morning:

The build system for Bioconda takes recipes and converts them into conda packages that are uploaded to anaconda.org as well as Docker containers that are uploaded to quay.io as part of the Biocontainers project.

https://bioconda.github.io/contributor/build-system.html

What this measns is that we can assume safely that there are bioconda-based docker and singularity containers for each bioconda package