[Enhancement]: better support for snapcraft push

[Saviq]

What changes would you like?

The only way I've found to push from this action is to run it again, with basename ${{ ...outputs.snap }}.

It would be nice if the action provided better facilities for that - maybe even publish on its own if publish-channel is provided?

Any extra information?

https://github.com/canonical/actions/blob/1d782d2578d57f083ca18a79cc165a313e67674d/build-snap/action.yml#L83-L97

You could also look at the review-tools bits I have in there ☝️, which would remain the last thing I did there above what your action does.