Copy Prometheus metrics implementation from jaeger-lib

[yurishkuro]

Follow-up to #3767:

• copy prometheus package from jaeger-lib
• refactor metrics builder
• make JLibAdapter private to expvar module (to be migrated in the follow-up PRs)
• add reverse adapter to jaeger-lib factory for use with jaeger-client-go (minimal dependency surface)

Partially addresses #3768

[codecov]

Codecov Report

Merging #3771 (c63da1a) into main (3d67ac8) will increase coverage by 0.00%.
The diff coverage is 99.31%.

@@           Coverage Diff            @@
##             main    #3771    +/-   ##
========================================
  Coverage   97.56%   97.57%            
========================================
  Files         282      287     +5     
  Lines       16426    16672   +246     
========================================
+ Hits        16026    16267   +241     
- Misses        317      321     +4     
- Partials       83       84     +1     

Impacted Files	Coverage Δ
internal/metrics/expvar/factory.go	0.00% <0.00%> (ø)
cmd/flags/service.go	100.00% <100.00%> (ø)
internal/metrics/expvar/adapter.go	100.00% <100.00%> (ø)
internal/metrics/jlibadapter/adapter.go	100.00% <100.00%> (ø)
internal/metrics/metricsbuilder/builder.go	100.00% <100.00%> (ø)
internal/metrics/prometheus/cache.go	100.00% <100.00%> (ø)
internal/metrics/prometheus/factory.go	100.00% <100.00%> (ø)
plugin/storage/badger/spanstore/reader.go	95.49% <0.00%> (-0.72%)	⬇️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 3d67ac8...c63da1a. Read the comment docs.