Build: Improve packaging

There was a problem with autodetection when there are multiple folders.

$ python -m build
* Creating virtualenv isolated environment...
* Installing packages in isolated environment... (setuptools>=61.0)
* Getting build dependencies for sdist...
error: Multiple top-level packages discovered in a flat-layout: ['myfolder', 'ethz_iam_webservice'].

To avoid accidental inclusion of unwanted files or directories,
setuptools will not proceed with this build.

If you are trying to create a single distribution with multiple packages
on purpose, you should not rely on automatic discovery.
Instead, consider the following options:

1. set up custom discovery (`find` directive with `include` or `exclude`)
2. use a `src-layout`
3. explicitly set `py_modules` or `packages` with a list of names

To find more information, look for "package discovery" on setuptools docs.

ERROR Backend subprocess exited when trying to invoke get_requires_for_build_sdist