Pulling Singularity containers using Azure Batch C# SDK

#### Feature Request Description
I'm building a cli tool that creates HPC pools on Azure. My main goal is to run Singularity containers pulled from ACR and run them inside the multi-node pools to execute complex (MPI, Cuda etc.) simulations.

I can perfectly run Docker containers. However, the same rationale failed when I tried to pull a Singularity container. In another discussion, https://github.com/Azure/acr/issues/411, I learned that Singularity containers are not supported on Batch Services.

As HPC people already know, Singularity solves some of the issues introduced by Docker on multi-node multi-tenant environments. So that would be nice to have feature.

Also, I'd like to know if there Is a potential workaround that you can suggest except using `batch-shipyard` which I already know.