Update readthedocs configuration

[ollipa]

Read The Docs made some breaking changes to their configuration file:
https://blog.readthedocs.com/migrate-configuration-v2/

This updates the configuration file and also adds support for Poetry in Read The Docs build. We know longer need separate requirements.txt file for docs.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (39f77f7) 100.00% compared to head (189ecec) 100.00%.

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Additional details and impacted files

@@            Coverage Diff            @@
##            master      #149   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            4         4           
  Lines          834       834           
=========================================
  Hits           834       834           

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