Use a rabbitmq to finalize pending payments

[LucasRouckhout]

Fixes #369

[codecov]

Codecov Report

Merging #370 (9db249a) into main (e89d6c2) will increase coverage by 4.85%.
The diff coverage is 61.44%.

❗ Current head 9db249a differs from pull request most recent head 8c01655. Consider uploading reports for the commit 8c01655 to get more accurate results

@@            Coverage Diff             @@
##             main     #370      +/-   ##
==========================================
+ Coverage   55.18%   60.03%   +4.85%     
==========================================
  Files          52       50       -2     
  Lines        3251     3213      -38     
==========================================
+ Hits         1794     1929     +135     
+ Misses       1263     1078     -185     
- Partials      194      206      +12     

Impacted Files	Coverage Δ
lib/service/config.go	0.00% <ø> (ø)
lib/service/invoices.go	70.55% <0.00%> (-0.21%)	⬇️
integration_tests/util.go	86.82% <50.00%> (-1.18%)	⬇️
rabbitmq/amqp.go	58.01% <58.01%> (ø)
rabbitmq/rabbitmq.go	55.77% <59.63%> (-8.03%)	⬇️
rabbitmq/mock_rabbitmq/rabbitmq.go	67.85% <67.85%> (ø)
lib/service/checkpayments.go	57.14% <78.57%> (+1.58%)	⬆️

... and 4 files with indirect coverage changes

[kiwiidb]

Minor nits, otherwise lgtm