Makes haddock3 restraints subcommands available as web service

[sverhoeven]

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In the haddock3 webapp I want to make a restraints file (*.tbl) from a list of active residues in 2 models/structures/molecules. I decided not to replicate that algorithm or have a complicated shell script behind a generic web service, but make the web service part of haddock3 repo. As the web service only exposes endpoints that are quick and do not need cns.

With this PR you can do

pip install fastapi uvicorn
uvicorn --port 5000 haddock.clis.restraints.webservice:app

This have the Swagger UI running at http://127.0.0.1:5000/docs#/