Please provide the list of revisions released on a given channel

[Facundo Batista]

The use case is basically "current release is broken, we want what we had before, which could be achieved by, knowing the history, re-releasing the previous one or any of the previous ones". Other way of getting this effect would be through an "unrelease" action, but "collecting some info" may be easier than "doing changes that affect charm state".

Note that it may be hard to know the previous one as releases may not happen by one person when the charm is managed by a team.

Also, something simpler than "the whole channel map history" may be enough for the use case, and much simpler to implement.

Related charmcraft issue: https://github.com/canonical/charmcraft/issues/919

Thanks!!