Allow to override changelog entry of the commit message in PR body

[marcoieni]

Motivations

Sometimes you want the commit message to be different in the git history and in the changelog.

Solution

We could allow to specify the commit message in the PR body. E.g. release-please allows this.
Example PR body:

BEGIN_COMMIT_OVERRIDE
feat: add my feature ..
END_COMMIT_OVERRIDE

Additional context

Not sure about the details, we probably need to think about this more, but I saw this feature and thought it was interesting to add 🤔