Honor `commit.verbose` configuration variable

It could be nice to have the same file content than when doing [`git commit`] to honor the settings, such as the [`commit.verbose`] configuration variable.

[`git commit`]: https://git-scm.com/docs/git-commit
[`commit.verbose`]: https://git-scm.com/docs/git-config#Documentation/git-config.txt-commitverbose