chore: Set up Sentry error catching

[frgfm]

This PR adds automatic error catching on all API calls, using Sentry SDK. This will be extremely useful to debug, since it provides the stack traces, the inputs, user information and everything you need to debug

Here is how it renders on Sentry after forcing a zero division error:

I already set the environment variables of the Sentry DNS on Heroku, so that we don't trigger this on our local dev versions!

Any feedback is welcome!

[codecov]

Codecov Report

Merging #71 (4c89203) into master (129ff9d) will decrease coverage by 1.49%.
The diff coverage is 33.33%.

@@            Coverage Diff             @@
##           master      #71      +/-   ##
==========================================
- Coverage   91.36%   89.87%   -1.50%     
==========================================
  Files          23       23              
  Lines         683      701      +18     
==========================================
+ Hits          624      630       +6     
- Misses         59       71      +12     

Flag	Coverage Δ
unittests	89.87% <33.33%> (-1.50%)	⬇️

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Impacted Files	Coverage Δ
src/app/main.py	61.11% <20.00%> (-15.82%)	⬇️
src/app/config.py	96.15% <100.00%> (+0.50%)	⬆️

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