Add Orchestrator's latency metrics to Kafka events

[leszko]

Add new Kafka event "discovery_results" with the following data:

[
   {
      "address":"0x4f83f45ca6afd4ec0df8ddfb3827de8ef9b91823",
      "latency_ms":"2",
      "url":"https://127.0.0.1:8936"
   },
   {
      "address":"04f83f45ca6afd4ec0df8ddfb3827de8ef9b91824",
      "latency_ms":"3",
      "url":"https://127.0.0.1:8937"
   }
]

This includes the latency from Gateway to each Orchestrator for each discovery process.

[gioelecerati]

Tests are failing because of latency apparently - other than that, looks good

[codecov]

Codecov Report

Attention: Patch coverage is 52.38095% with 10 lines in your changes missing coverage. Please review.

Project coverage is 32.16336%. Comparing base (1c1c280) to head (d43dfcb).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
discovery/discovery.go	52.38095%	9 Missing and 1 partial ⚠️

Additional details and impacted files

@@                 Coverage Diff                 @@
##              master       #3391         +/-   ##
===================================================
+ Coverage   32.15960%   32.16336%   +0.00376%     
===================================================
  Files            147         147                 
  Lines          40753       40770         +17     
===================================================
+ Hits           13106       13113          +7     
- Misses         26874       26883          +9     
- Partials         773         774          +1     

Files with missing lines	Coverage Δ
common/types.go	0.00000% <ø> (ø)
discovery/discovery.go	86.30137% <52.38095%> (-5.94669%)	⬇️

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Files with missing lines	Coverage Δ
common/types.go	0.00000% <ø> (ø)
discovery/discovery.go	86.30137% <52.38095%> (-5.94669%)	⬇️