Fix documentation build

[epassaro]

Description

This is a continuation of @smithis7 PR #1387

• Cleared notebook outputs (large diffs!)
• Fixed softlinks (removed all files under schemas and make a link to the folder)
• Add channel: conda-forge to workflow (again)
• Pin sphinxcontrib-bibtex (see here)

Motivation and Context

Documentation build is failing repeatedly. Maybe due to some incompatibility with WSL symlinks (see here).

How Has This Been Tested?

See: https://github.com/epassaro/tardis/actions/runs/425646553

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have assigned/requested two reviewers for this pull request.

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[codecov]

Codecov Report

Merging #1392 (caa315c) into master (575c228) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1392   +/-   ##
=======================================
  Coverage   72.38%   72.38%           
=======================================
  Files          66       66           
  Lines        5098     5098           
=======================================
  Hits         3690     3690           
  Misses       1408     1408           

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