Support dynamic version attribute in setup.cfg

[danielhollas]

In my app's setup.cfg I have version = attr: aiidalab_ispg.__version__, which I believe is valid and pip recognizes it, but aiidalab list says

App name               Version                          Path
---------------------  -------------------------------  ---------------------------------------
aiidalab-ispg          attr: aiidalab_ispg.__version__  /home/jovyan/apps/aiidalab-ispg

[danielhollas]

Currently we use configparse.ConfigParser to parse the setup.cfg file.

aiidalab/aiidalab/metadata.py

Line 38 in f865490

def _parse_setup_cfg(setup_cfg):

To support dynamic attributes, we can use the setuptools API directly, per
https://stackoverflow.com/a/71276404/3682277