feat: Adds proper APM using Prometheus and Grafana

[frgfm]

This PR introduces the following modifications:

• adds Prometheus & grafana for application performance monitoring
• updates CI accordingly

Here is how it renders:

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (6995b12) 82.55% compared to head (e30bb9a) 82.59%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #52      +/-   ##
==========================================
+ Coverage   82.55%   82.59%   +0.03%     
==========================================
  Files          29       29              
  Lines         969      971       +2     
==========================================
+ Hits          800      802       +2     
  Misses        169      169              

Flag	Coverage Δ
unittests	82.59% <100.00%> (+0.03%)	⬆️

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