Edit commit message with config file

Problem

There currently isn't a way to edit the commit message that is created when you run pycalver bump. This can be seen on this line where the commit message is hardcoded. https://gitlab.com/mbarkhau/pycalver/-/blob/master/src/pycalver/cli.py#L242

Acceptance Criteria

• By default, the commit message will still be bump version to {new_version}
• A new option called commit_message which can take in a string
• User should also be able to input the different pycalver placeholders such as {pep440_version}, {pycalver} etc.