[RFR] Avoid contacting twice (Fixes #28)

[thomaspaulb]

Attempt to revive #29

Depends on:

• Drop support for other configuration file formats than yaml #76

[codecov]

Codecov Report

❌ Patch coverage is 83.95062% with 13 lines in your changes missing coverage. Please review.
✅ Project coverage is 81.61%. Comparing base (fe1e0bb) to head (9016ee7).
⚠️ Report is 17 commits behind head on master.

Files with missing lines	Patch %	Lines
git_aggregator/repo.py	83.95%	13 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #74      +/-   ##
==========================================
- Coverage   82.64%   81.61%   -1.03%     
==========================================
  Files           6        6              
  Lines         409      457      +48     
==========================================
+ Hits          338      373      +35     
- Misses         71       84      +13     

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[thomaspaulb]

Seems like the only cause for keeping this open is #28