Update Read the Docs configuration and add graphviz dependency

[namurphy]

• Fixes Documentation bug with inheritance diagrams #1838 by adding a graphviz dependency (see also Broken examples of sphinx.ext.inheritance_diagram sphinx-doc/sphinx#10948 and RTD builder: add graphviz depedendency sphinx-doc/sphinx#11040) in order to fix a problem with inheritance diagrams not showing up in the doc build
• Updates the Read the Docs configuration file
  • Adds a link to the troubleshooting guide
  • Sets fail_on_warning to true which is equivalent to the settings we have for the CI doc build
• Corrects the link anchor to the troubleshooting guide in tox.ini

[github-actions]

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[codecov]

Codecov Report

Base: 98.33% // Head: 98.33% // No change to project coverage 👍

Coverage data is based on head (e64c9db) compared to base (c61da87).
Patch has no changes to coverable lines.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1840   +/-   ##
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  Coverage   98.33%   98.33%           
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  Files          95       95           
  Lines        8343     8343           
=======================================
  Hits         8204     8204           
  Misses        139      139           

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[namurphy]

• Check that the inheritance diagrams show up correctly in on detector stacks page

[namurphy]

This adds the -W --keep-going flags to the doc build, which are used in the build_docs tox environment.