feat: extract info on calculations/workflows

[ltalirz]

For plugins that can be installed successfully, inspect the process
classes provided by them (similar to what verdi plugin does) and store
this information in a local json file.

This is in preparation of a more detailed information shown on
the registry.

Also:

• Switch installation tests to aiida-core docker container in order to
  get a clean install every time.

[ltalirz]

It's not clear to me

• why this job can be "skipped"
• why no output is being produced
• what is causing the issues the second time we try to create a container (from here it looked like the first time we create the container everything runs fine).

[ltalirz]

I'm going to merge this, even if the github action still fails.

If it turns out it can't be made to work, we'll need to figure out something else.