Singularity/Apptainer support

[pdiakumis]

Adding initial support for Singularity/Apptainer. I have no idea if the final product of this works yet, will test next week.

• .github/workflows/build_conda_recipes.yaml:

  • I am first freeing up disk space since the Docker container + SIF image fill that up.
  • Under the docker/build-push-action Action I use the load: true parameter to keep the Docker image on the machine, else it gets deleted.
  • Under the Apptainer Build section, I first save the Docker image as a tar file, then I build a SIF file using apptainer build.
  • I am then uploading the SIF file to the repo's GitHub Container Registry.

• .github/workflows/apptainer.yaml:

  • Keeping the apptainer chunk in this file for easier debugging.

• Also see Is it possible to view singularity images as oras://ghcr.io/ in github packages singularityhub/github-ci#16 (comment) for the bug in the GHCR interface.

• And related to Sif image  #218.

[sigven]

Solid work!