feat: add an upload diff endpoint for adhoc mode.

[abeaumont]

This is part of #784.

[github-actions]

size-limit report 📦

Path	Size	Loading time (3g)	Running time (snapdragon)	Total time
webapp/public/assets/app.js	575.35 KB (0%)	11.6 s (0%)	1.4 s (+8.53% 🔺)	12.9 s

[codecov]

Codecov Report

Merging #839 (7d27055) into main (02b9703) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main     #839   +/-   ##
=======================================
  Coverage   70.44%   70.44%           
=======================================
  Files          71       71           
  Lines        2523     2523           
  Branches      458      458           
=======================================
  Hits         1777     1777           
  Misses        718      718           
  Partials       28       28           

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[pyroscopebot]

Screenshots

Throughput

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