feat(zipkin): allow to configure url via environment #1675

[vmarchaud]

allow to configure zipkin via environment according to the spec: https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/sdk-environment-variables.md#zipkin-exporter

[codecov]

Codecov Report

Merging #2097 (190d9be) into main (115ee39) will increase coverage by 0.01%.
The diff coverage is 100.00%.

❗ Current head 190d9be differs from pull request most recent head f6018be. Consider uploading reports for the commit f6018be to get more accurate results

@@            Coverage Diff             @@
##             main    #2097      +/-   ##
==========================================
+ Coverage   92.73%   92.75%   +0.01%     
==========================================
  Files         138      138              
  Lines        4928     4927       -1     
  Branches     1017     1017              
==========================================
  Hits         4570     4570              
+ Misses        358      357       -1     

Impacted Files	Coverage Δ
...ckages/opentelemetry-core/src/utils/environment.ts	100.00% <ø> (ø)
...ckages/opentelemetry-exporter-zipkin/src/zipkin.ts	100.00% <100.00%> (ø)
...emetry-core/src/platform/node/RandomIdGenerator.ts	93.75% <0.00%> (+6.25%)	⬆️

[dyladan]

Don't mind the close and reopen. was an accident. there are conflicts