Support digest for input image in userspace converter

[tianouya-db]

What is the version of your Accelerated Container Image

1.0.2

What would you like to be added?

The userspace converter requires an --input-tag to identify the image the convert (USERSPACE_CONVERTOR.md). Is it possible to use the digest to identify the input image? This can be supported as an alternative to --input-tag.

-i, --input-tag string          tag for image converting from (required)

Why is this needed for Accelerated Container Image?

1. A tag can be volatile
2. Sometimes the client has access to the digest but not the tags on the image to convert

Supporting a digest parameter would be an enhancement.

Are you willing to submit PRs to contribute to this feature?

• [X] Yes, I am willing to implement it.