testutil/promrated: implement rated fetching and reporting

[LukeHackett12]

Adds fetching of rated effectiveness and making these metrics available to prometheus.

category: misc
ticket: #1540

[codecov]

Codecov Report

Base: 54.16% // Head: 53.96% // Decreases project coverage by -0.19% ⚠️

Coverage data is based on head (46232b0) compared to base (708c345).
Patch coverage: 40.81% of modified lines in pull request are covered.

❗ Current head 46232b0 differs from pull request most recent head bf47a5d. Consider uploading reports for the commit bf47a5d to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1569      +/-   ##
==========================================
- Coverage   54.16%   53.96%   -0.20%     
==========================================
  Files         156      157       +1     
  Lines       19626    19717      +91     
==========================================
+ Hits        10630    10641      +11     
- Misses       7558     7630      +72     
- Partials     1438     1446       +8     

Impacted Files	Coverage Δ
testutil/promrated/prometheus.go	42.02% <0.00%> (ø)
testutil/promrated/promrated.go	0.00% <0.00%> (ø)
testutil/promrated/rated.go	57.14% <57.14%> (ø)
core/qbft/qbft.go	73.73% <0.00%> (-10.09%)	⬇️
app/monitoringapi.go	81.45% <0.00%> (+0.15%)	⬆️
cmd/bootnode/p2p.go	38.31% <0.00%> (+0.24%)	⬆️
app/app.go	64.32% <0.00%> (+0.70%)	⬆️
core/priority/prioritiser.go	61.69% <0.00%> (+2.82%)	⬆️
app/vmock.go	77.72% <0.00%> (+3.62%)	⬆️

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