converts Resource into a target_info metric on the prometheus exporter

[paivagustavo]

Implements the required conversion of a metricResource so it can be exported by the prometheus exporter, specs.

The prometheus client lib doesn't have a info metric type, hence the usage of a gauge metric as suggested by the specs.

Fixes #3166, #3271

[codecov]

Codecov Report

Merging #3285 (668093b) into main (05aca23) will increase coverage by 0.0%.
The diff coverage is 91.1%.

Additional details and impacted files

@@          Coverage Diff          @@
##            main   #3285   +/-   ##
=====================================
  Coverage   77.8%   77.9%           
=====================================
  Files        164     164           
  Lines      11289   11319   +30     
=====================================
+ Hits        8791    8821   +30     
  Misses      2301    2301           
  Partials     197     197           

Impacted Files	Coverage Δ
exporters/prometheus/exporter.go	83.0% <89.6%> (+1.2%)	⬆️
exporters/prometheus/config.go	100.0% <100.0%> (ø)
exporters/jaeger/jaeger.go	90.3% <0.0%> (-0.9%)	⬇️
sdk/trace/batch_span_processor.go	81.9% <0.0%> (+1.7%)	⬆️

[MrAlias]

A user may register the exporter with multiple exporters or other sources that generate a target info metric. An option to disable the target info metric should be include for the exporter to prevent multiple from being generated.