Upload to charmhub branches for all cases, not just for git branches named /branch/...

[ca-scribner]

Rather than selectively uploading intermediate work to charmhub branches (eg: latest/edge/someBranch), we could upload all PR updates to charmhub. charmhub branches are ephemeral (ttl=30day) anyway so it won't make too much garbage, and this way we can easily test deployments.

There might be some logic that needs working through as we still need to know the destination track/channel that the branch should go to, but this could be the same as we currently use (if git branch is called /track/..., push to charmhub at /track/edge/branchName, else push to latest/edge/branchname)

[simskij]

Yeah, this change makes sense to me!

[ca-scribner]

If there's any worry about always publishing to branches, a compromise would be an optional upload-to-branch-label argument (or something with a better name). If set, then the action would only upload to branches if the PR has that label (this way PRs can opt-in to branch publishing when it is needed). If unset, then the action would always publish to a branch

[simskij]

I think it's fine without that extra precaution as remote PRs won't have access to secrets and hence will fail, so to have this work, repos that want to publish to branches will have to enforce a feature branch based workflow rather than forks.