Add "etelemetry" to singularity_cmd

[yarikoptic]

• Add to singularity_cmd
  • @satra could you give curl command example for querying etelemetry for a new version?
• There is no PyPI package to test versions against -- we would probably need to make it more sophisticated as to checks for a container version of containers we index here. To simplify we can establish index of most recent versions per container and make etelemetry capable of fetching/using it.