Add support for parsing echcheck related metadata in pipeline

[hynnot]

Issue #108

[codecov]

Codecov Report

Attention: Patch coverage is 96.72131% with 2 lines in your changes missing coverage. Please review.

Project coverage is 82.58%. Comparing base (853ada2) to head (22f3e49).
Report is 21 commits behind head on main.

Files with missing lines	Patch %	Lines
...e/src/oonipipeline/transforms/nettests/echcheck.py	90.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #115      +/-   ##
==========================================
+ Coverage   82.21%   82.58%   +0.37%     
==========================================
  Files          69       71       +2     
  Lines        4166     4227      +61     
==========================================
+ Hits         3425     3491      +66     
+ Misses        741      736       -5     

Flag	Coverage Δ
oonidata	77.50% <100.00%> (+0.24%)	⬆️
oonipipeline	86.85% <95.00%> (+0.45%)	⬆️

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[hellais]

This looks great! Thanks for putting it together. Merging.