Dry run mode that only prints the changelog as a preview

[fengelniederhammer]

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