Improve readability of autogenerated release notes

[cortadocodes]

Contents (#70)

Enhancements

• Use collapsible sections in upgrade section and add breaking change emoji to denote each section
• Put upgrade instructions at bottom of release notes
• Move breaking change warning to contents section
• Add horizontal rule between contents and upgrade instructions
• Use H1 for contents and upgrade instructions headers

Refactoring

• Factor out contents section creation into method

[codecov-commenter]

Codecov Report

Merging #70 (b593a81) into main (60ee80b) will increase coverage by 0.05%. The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main      #70      +/-   ##
==========================================
+ Coverage   97.21%   97.26%   +0.05%     
==========================================
  Files           4        4              
  Lines         287      293       +6     
==========================================
+ Hits          279      285       +6     
  Misses          8        8              

Impacted Files	Coverage Δ
conventional_commits/compile_release_notes.py	96.75% <100.00%> (+0.13%)	:arrow_up:

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