Getting the branch in prepare for multiple releases

**Is your feature request related to a problem? Please describe.**
What I'm trying to achieve is setting the `next` and `latest` tags based on branches. I want ship.js to trigger a new `latest` release when on branch `main` & `next` release when on branch `next`.

**Describe the solution you'd like**
Ability to modify the publishCommand by using git branches

**Describe alternatives you've considered**
N/A.

**Additional context**
N/A.

Start by tracing ship.js's publishCommand and how the current release branch or tag is selected. Compare the requested main-to-latest and next-to-next behavior, then verify that releases from each branch produce the corresponding tag.

Written by the indexing model from the issue text.