feat(containers): support build args

[cyclimse]

Summary

What's changed?

• Add support for buildArgs as proposed in Add support for buildArgs option when building container images with the directory option #317
• Fix an annoying bug with registry auth: the config used to log in to registry was not the same as the one being tested, leading to silent push errors

Why do we need this?

• It's indeed not ideal to not provide

How have you tested it?

• Tested manually ✅

Checklist

• I have reviewed this myself
• There is a unit test covering every change in this PR
• I have updated the relevant documentation

Details

Closes #317

[cyclimse]

For reviewers, I have no idea how we never ran into it before, but this currently is not functional.

auth is sent to PushOptions as is, with a username/password field. This obviously is not recognized as valid options, so the auth here is not used for pushing.

This is especially annoying because we do a checkAuth initially but it ends up being useless as those credentials are not used for pushing

Instead, the local docker credentials in ~HOME/. docker/config.json are used. I ran into this because my local credentials were invalid and I couldn't understand why somehow checkAuth was working but my push was silently failing.