Add Changelog to Sphinx Docs

[afshin]

• Copy the changelog into the docs source when building
• Use the MyST parser for markdown files
• Clean up docs requirements files

[codecov-io]

Codecov Report

Merging #465 (92ed13d) into master (9d79ef9) will decrease coverage by 0.02%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #465      +/-   ##
==========================================
- Coverage   77.81%   77.79%   -0.03%     
==========================================
  Files         106      106              
  Lines        9127     9127              
  Branches      976      976              
==========================================
- Hits         7102     7100       -2     
- Misses       1676     1677       +1     
- Partials      349      350       +1     

Impacted Files	Coverage Δ
jupyter_server/services/kernels/kernelmanager.py	80.31% <0.00%> (-0.79%)	⬇️

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