Allow publishing Kueue images prior to merge to the main branch

[mimowo]

What would you like to be added:

I would like to be able to push some images prior to the publication to the main branch.

We certainly don't want to push all branches, so I would propose to modify the rules for publishing here using a dedicated entry "^push-prototype-". Users who would want to push their branches would use this prefix to their branch names.

Actually, there is already a workaround by naming the branch with the release- prefix, but it does not capture the intention.

Why is this needed:

To be able to hand an image to a user for testing.

This is inspired by discussions around #4165, but there are other cases where we have a "design partner" and being able to share them an image from branch would be great.

[mimowo]

cc @tenzen-y @gabesaba @dgrove-oss @BenTheElder wdyt?

[mimowo]

Actually, I just realized, looking at the rules, there is already a workaround by naming the branch with the release- prefix, but it does not capture the intention, and I believe this is a valid use-case, not something we need to be "securing" by obfuscation :)

[mimowo]

cc @PBundyra

[tenzen-y]

Could we prepare a separate dedicated dir or tag prefix something like pre-${IMAGE_HASH}? Because in general, the latest image is recognized as the main branch (merged) image.

[mimowo]

This would be ideal, but not sure how much work this would be. Maybe an acceptable solution which is "in the middle" is to don't push such images with the "latest" tag.