allow publish charm on feature branches about charming-actions HOT 2 CLOSED

I think the idea when written was that:

• ch:latest/edge is related to gh:main
• a PR from gh:branch1 against gh:main logically then goes to ch:latest/edge/branch1
• a PR from gh:branch1 against gh:someOtherBranch felt strange to put in ch:latest/edge/branch1 because it wasn't related to gh:main
• it might make sense for a PR from gh:branch1 against gh:someOtherBranch to publish to ch:someOtherBranch/edge/branch1, but that charmhub track often doesn't exist

But, I think @beliaev-maksim brings up a great point: it doesn't really matter what the target of the PR is - the source branch is what matters. So just lumping them all in ch:latest/edge/... doesn't cause a problem

...technically maybe it could cause a problem in some edge case where a PR isn't rebased properly? But that seems like something we shouldn't defend against

from charming-actions.

While we're at it, we could I think get rid of all the logic around this channel choosing. prs against gh:track/* can just get lumped into the same place, too

from charming-actions.