Add support for podman image digests

[mjrlee]

Adds a new "engine" build argument that can be used to handle podman's different way of handing image digests.

Fixes #3170

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the Apache 2.0 License.

[github-actions[bot]]

🍕 Here are the new binary sizes!

Name	New size (kiB)	size (kiB)	Delta (%)
macOS (amd)	51492	51488	+0.01
macOS (arm)	51680	51684	❤️ -0.01
linux (amd)	45324	45324	❤️ 0.00
linux (arm)	43584	43588	❤️ -0.01
windows (amd)	42144	42144	❤️ 0.00

[ammerzon]

@mjrlee, are there any updates on this, or do you need support? 😁

[mjrlee]

Sorry, I haven't had much time to look at this recently.

I can confirm I'm currently using it with podman and it's working well.

I've resolved a couple of comments on the PR, and replied to another.