feat: add support for Singularity media types
Related to #621 (closed). Adds support for media types found here: https://github.com/apptainer/singularity/blob/master/internal/pkg/client/oras/oras.go#L47:L55
Related to #621 (closed). Adds support for media types found here: https://github.com/apptainer/singularity/blob/master/internal/pkg/client/oras/oras.go#L47:L55