chore: add a config file for git cliff

notable changes are:

• decrease heading level by one since we do not carry a global changelog
• show the scope of each change so that the changelog entries have some more context

See the example differences here:

Without this commit

# Changelog

All notable changes to this project will be documented in this file.

## [1.0.5] - 2023-07-22

### Bug Fixes

- Use correct version variable for release target

### Features

- Use a unique scope name instead of --keep-unit

### Miscellaneous Tasks

- Fix spelling mistake packge -> package
- Simplify args construction for systemd-nspawn
- Add a config file for git cliff

<!-- generated by git-cliff -->

With this commit:

# [1.0.5] - 2023-07-22

## Bugfixes

- make: Use correct version variable for release target


## Features

- arch-nspawn: Use a unique scope name instead of --keep-unit


## Miscellaneous Tasks

- arch-nspawn: Simplify args construction for systemd-nspawn
- Add a config file for git cliff
- Fix spelling mistake packge -> package


<!-- generated by git-cliff -->