Simplify setup for local development dependencies

Currently, the main package requires the mysqlclient, which may also need additional header files to be installed.
When working from docker, or when only editing documentation, this dependency isn't necessary.
Unfortunately, there is no way to install just optional dependencies without installing the core dependencies.
Still, I want an easier way that someone can get started working on the repository. At the very least, pre-commit should still be locally installed. Maybe we can specify (some of) the development dependencies in a just file or similar instead.

This also affects the way we have CI pipelines, for example the documentation building pipeline now has a repeated list of documentation dependencies, which is an easy oversight.

Inspect the main package dependency configuration, the documentation-building CI pipeline, and the local development setup. Start by tracing why installing the package requires mysqlclient and how documentation dependencies are repeated in CI. Done means a contributor can install the needed development or documentation dependencies without unnecessary database headers, while pre-commit remains available and CI uses the same dependency definition.