Enhanced Singularity Support

[alfpark]

Enhance Singularity support. Continuing feature expansion from initial support.

• Migrate to support Singularity 3 (targeting 3.3.0)
  • Break cascade into Docker-specific and Singularity-specific paths
• Support SIF ORAS-based images in ACR
• Augment pool images list to support Singularity images (where the container runtime is installed)
• Improve MPI mechanics (Improve MPI Interface/Mechanics #287)
• Update README and docs

Lower-priority work:

• Image auto-verification support?
• Debian host OS support

[JonShelley]

Any update on when this capability is targeted for delivery?

[alfpark]

This workitem will be delayed until after Singularity 3.x is released. Fixes to the current Singularity support will continue in the meantime.

[ArangoGutierrez]

Heya any updates on this work item? singularity has already 3.1 and 3.2 releases and a Sylabs supported 3.1 release.

I would be happy to help on this work item.

I Volunteer :)

[alfpark]

Thanks for offering to help - this item will be delayed a bit further after some alignment takes place.

[alfpark]

Work is scoped and started.

cc @vincentlabonte