Fastapi based API

[hellais]

This implements: #35

This branch is based on top of #44. That one should be merged before this one is ready to be landed in master.

[codecov]

Codecov Report

Attention: Patch coverage is 65.34653% with 140 lines in your changes are missing coverage. Please review.

Project coverage is 81.40%. Comparing base (b3f354d) to head (be5a1c5).
Report is 2 commits behind head on main.

Files	Patch %	Lines
oonidata/fastapi/routers/observations.py	0.00%	80 Missing ⚠️
oonidata/fastapi/routers/aggregation.py	73.10%	32 Missing ⚠️
oonidata/fastapi/routers/measurements.py	80.00%	27 Missing ⚠️
oonidata/fastapi/dependencies.py	75.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #45      +/-   ##
==========================================
- Coverage   82.43%   81.40%   -1.03%     
==========================================
  Files          78       86       +8     
  Lines        6307     6711     +404     
==========================================
+ Hits         5199     5463     +264     
- Misses       1108     1248     +140     

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[hellais]

I cherry picked 2d9e6d5 directly into master so this is only changes related to fastapi.

We should probably move this branch into ooni/backend in the oonidataaapi package.