Incorporating old physics section of the documentation

[isaacgsmith]

This pull request incorporates the "old physics" section of the documentation into the updated physics section.

Description

Changes include:

• Including doppler shift graph in docs/physics/montecarlo/propogation.rst.
• Including tau_sobolev section and a summary of BasePlasma in docs/physics/plasma/index.rst.
• Some minor changes in docs/physics/plasma/index.rst to give more context to the pages linked in toctrees.
• Deleted docs/physics/old_physics/ and removed it from the toctree in ``docs/index.rst```.

Motivation and Context

This pull request addresses issue #1422.

How Has This Been Tested?

• Testing pipeline
• Reference Data Comparison following these instructions
• Other (please describe)

I built the docs locally and made sure that no new warnings occurred.

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)
• None of the above (please describe)

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 built the documentation on my fork following these instructions
• I have assigned and requested two reviewers for this pull request

[codecov]

Codecov Report

Merging #1470 (eaab28d) into master (50f13ba) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1470   +/-   ##
=======================================
  Coverage   71.13%   71.13%           
=======================================
  Files          67       67           
  Lines        5523     5523           
=======================================
  Hits         3929     3929           
  Misses       1594     1594           

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[jaladh-singhal]

Thanks for this very essential PR - docs are neater now. Plasma section looks great.

And for montecarlo section, @smithis7 I'm assuming that you have confirmed with @wkerzendorf and/or @andrewfullard that we don't need anything except doppler shift graph from old documentation?

[andrewfullard]

Will merge once the tests pass

[isaacgsmith]

Will merge once the tests pass

Apparently the tests did not pass. I'm not entirely sure why.