export ToZipkinSpanModels for use outside this library

[coryb]

I recently started using OpenTelemetry and need to publish to an internal Zipkin compatible service without using the normal http service. There is a lot of useful code in this package for converting the spans I am hoping to be able to reuse this library rather than copy/paste it into my project.

Thanks for your consideration!

[linux-foundation-easycla]

The committers are authorized under a signed CLA.

• ✅ coryb (aa06b68)

[codecov]

Codecov Report

Merging #2027 (854b21f) into main (d5d4c87) will increase coverage by 0.0%.
The diff coverage is 100.0%.

@@          Coverage Diff          @@
##            main   #2027   +/-   ##
=====================================
  Coverage   72.7%   72.7%           
=====================================
  Files        164     164           
  Lines       8079    8079           
=====================================
+ Hits        5876    5880    +4     
+ Misses      1974    1972    -2     
+ Partials     229     227    -2     

Impacted Files	Coverage Δ
exporters/zipkin/model.go	99.1% <ø> (ø)
exporters/zipkin/zipkin.go	70.1% <100.0%> (ø)
sdk/metric/sdk.go	81.3% <0.0%> (+1.1%)	⬆️
sdk/metric/refcount_mapped.go	100.0% <0.0%> (+22.2%)	⬆️