This PR fixes readthedocs documentation for the newly named deeprank2 package. In particular:

• as mentioned here, readthedocs builds without a configuration file are now deprecated. I added a .readthedocs.yml file to address it. The specific dependencies needed are now specified in docs/requirements.txt, as indicated in the newly added .yml file.
• I updated a .md parser dependency to myst-parser as indicated here, since recommonmark won't be maintained anymore and is now deprecated.
• I removed setuptools.config.read_configuration from docs/conf.py since it's now deprecated. We're now using configparser.ConfigParser().
• I fixed the remaining old namings using the new deeprank2 nomenclature.