Feature/5.0 schema

[hellais]

This PR implements schema changes in preparation for 5.0.0 release

see:

• Improve schema of obs_* tables in preparation for 5.0.0-rc.0 #88
• Come up with better way of storing and generating control measurements #92
• Create tables for storing metadata about targets #89
• Improve performance of the DELETE operation on observation generation #87

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 77.51%. Comparing base (ff1fc86) to head (573321b).

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #94      +/-   ##
==========================================
- Coverage   82.14%   77.51%   -4.64%     
==========================================
  Files          82       32      -50     
  Lines        6351     1921    -4430     
==========================================
- Hits         5217     1489    -3728     
+ Misses       1134      432     -702     

Flag	Coverage Δ
oonidata	77.51% <100.00%> (+0.07%)	⬆️
oonipipeline	?

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