Dry run mode that only prints the changelog as a preview

Quite often, I would like to preview the changelog that the commits in my PR will result in. It would be nice to run release-please in a mode that prints the changelog.

I imagine a GitHub Actions workflow:
* Run release-please to generate the changelog
* (Optionally check whether there are relevant changes)
* Post the changelog to a comment in the PR, so that the author knows whether the next release will look as intended.

The missing bit is getting the changelog. (Sorry, if I missed an existing feature, I didn't find anything in the docs.)

**Is your feature request related to a problem? Please describe.**
No.

**Describe the solution you'd like**
A CLI flag that only prints the generated changelog would be cool. Similar to what `--dry-run` does, but without all the other clutter.

**Describe alternatives you've considered**
Using `--dry-run` and somehow extracting the changelog from there.

**Additional context**