Make publish function async

[edelabar]

From JohnSundell#141:

The internal semaphore used to make the CLI wait for publish to finish is no longer necessary and causes problems with concurrency. This PR removes it and makes the publish function async.

• Is no longer necessary because Swift already supports async main, so one can build CLIs that use async and automatically await for the work to finish.
• It cause problems because is blocking the main thread. If any async code needs to run on the MainActor this causes a deadlock.

[edelabar]

I like the concept but it breaks the tests and it doesn't look like an easy fix so needs research...