Multiple paths for different version of Singularity images in recipe yaml file

[gq1]

Currently you can add singularity image directly from command:

  # Add a SIF container to the registry namespace
  # After adding, you would edit the container.yaml

  $ shpc add salad_latest.sif dinosaur/salad:latest

But if you want to add the second version of the same software, the new tag will be added but the path will be overwritten, ending with both the new version and the old version will use the same image:

latest:
  0.5.4: sha256:a671c879b5242a9b08254d3075cc9c103a31f402f734b8e2b904f1029f9a5a91
tags:
  0.4.0: sha256:d089d5e12127231cb0e161d901a3e83c66dcfede344024c664f4b39057a69b25
  0.5.4: sha256:a671c879b5242a9b08254d3075cc9c103a31f402f734b8e2b904f1029f9a5a91
path: sha256:a671c879b5242a9b08254d3075cc9c103a31f402f734b8e2b904f1029f9a5a91.sif
aliases:
  gx: /app/bin/gx

[vsoch]

I think we would want to make sure that the path is derived as simply the digest with sif. If you want to open a PR to work on it I'd be happy to review.