Preheat to support singularity image format

[mfarooq-tech]

Feature request:

Currently, singularity image format download is not supported by preheating.

Singularity image pull sequence: https://github.com/apptainer/apptainer/blob/main/internal/pkg/client/oras/oras.go

Use case:

UI Example:

[gaius-qi]

Fix #769

[yxxhero]

@mfarooq-intel can you give me a example for singularity image format.

[embroede]

Here are some examples: https://cloud.sylabs.io/library/tjlhx253/default/tensorflow

Or an image can be built from scratch by following the Singularity quick start guide here: https://docs.sylabs.io/guides/latest/user-guide/quick_start.html