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

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)