Refactor dependency management to pyproject.toml

[s-heppner]

Previously, our dependency management was a bit of a mess. We had both a requirements.txt and a pyproject.toml and some dependencies were only defined in one but not the other, leading to a lot of problems.

This aims to fix this mess and refactor towards only using pyproject.toml to define the dependencies.

At the same time, we also clean up the install process, which now works by simply calling pip install . or pip install -e .[dev] for the developer envrionment. This change is reflected in the .github/workflows.

Furthermore, we configure the already introduced setuptools_scm to automatically infer a version based on the most recent git tag.

Fixes #301
Fixes #303
Fixes #306

[s-heppner]

After a lot of research regarding dependency management, I think I've come up with the proper way of using pyproject.toml and requirement.txt. Both seem to have their use cases and this stackoverflow discussion was especially useful to understanding the differences:

• pyproject.toml is used to define everything needed in theory to build a package. This comes without strict pinning of versions so that the build system can choose the optimal versions if, for example different dependencies depend on different versions of the same package.
• requirements.txt is used to create reproducible builds, especially for CI pipelines. It's a concrete set of instructions to pip which packages to install and usually contains pinned dependency versions.

Since we've not used pinned dependencies before (and to pin or not to pin is a whole other discussion that we shan't open right now), we do not have a need the requirements.txt anymore.

Instead, pip is smart enough to use the pyproject.toml to search for the dependencies. It now also became easier to install. As a user, wanting to use a local install of the SDK, we can now simply do:

pip install . 

and use the SDK (from basyx.aas import model).

If we are a developer on the SDK itself, we might want to install it dynamically (-e) and also install the additional developer requirements ([dev]:

pip install -e .[dev]

I've adapted the CI pipelines to do this as well. I've also changed the CONTRIBUTING.md instructions.

[Frosty2500]

LGTM, I see no problems 👍
I dont have write access so someone else will have to merge this branch