Update Custom HTTP Routes Documentation

[misscoded]

Summary

Update Custom HTTP Routes section of documentation to include the newly introduced way to add custom routes. Move ExpressReceiver approach to its own (accordion) section.

Requirements (place an x in each [ ])

• I've read and understood the Contributing Guidelines and have done my best effort to follow them.
• I've read and agree to the Code of Conduct.

[codecov]

Codecov Report

Merging #1136 (39eba05) into main (ef7ce04) will not change coverage.
The diff coverage is n/a.

❗ Current head 39eba05 differs from pull request most recent head 2ae7c05. Consider uploading reports for the commit 2ae7c05 to get more accurate results

@@           Coverage Diff           @@
##             main    #1136   +/-   ##
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  Coverage   71.71%   71.71%           
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  Files          15       15           
  Lines        1354     1354           
  Branches      402      402           
=======================================
  Hits          971      971           
  Misses        312      312           
  Partials       71       71           

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[filmaj]

🍾

[srajiang]

Looks good! I left some small suggestions.