Support Resources in ZipkinExporter

[CodeBlanch]

Changes

ZipkinExporter will now take service name from Resource if set and apply any Resource attributes as tags on outgoing spans. This brings it into parity with JaegerExporter w.r.t. Resources.

TODO

• CHANGELOG.md updated for non-trivial changes
• Changes in public API reviewed

[codecov]

Codecov Report

Merging #1385 into master will increase coverage by 0.10%.
The diff coverage is 90.00%.

@@            Coverage Diff             @@
##           master    #1385      +/-   ##
==========================================
+ Coverage   81.18%   81.29%   +0.10%     
==========================================
  Files         226      226              
  Lines        6081     6094      +13     
==========================================
+ Hits         4937     4954      +17     
+ Misses       1144     1140       -4     

Impacted Files	Coverage Δ
...plementation/ZipkinActivityConversionExtensions.cs	98.88% <ø> (+6.65%)	⬆️
...y.Exporter.Zipkin/Implementation/ZipkinEndpoint.cs	80.48% <71.42%> (-0.60%)	⬇️
...rc/OpenTelemetry.Exporter.Zipkin/ZipkinExporter.cs	85.71% <91.17%> (-0.19%)	⬇️
...rc/OpenTelemetry.Exporter.Jaeger/JaegerExporter.cs	84.94% <100.00%> (ø)
src/OpenTelemetry.Exporter.Jaeger/Process.cs	81.25% <100.00%> (ø)
...metry.Exporter.Zipkin/Implementation/ZipkinSpan.cs	95.50% <100.00%> (+0.10%)	⬆️
src/OpenTelemetry/Trace/ActivityExtensions.cs	100.00% <100.00%> (+20.00%)	⬆️
...emetry.Api/Internal/OpenTelemetryApiEventSource.cs	61.76% <0.00%> (-2.95%)	⬇️
...us/Implementation/PrometheusExporterEventSource.cs	72.72% <0.00%> (+9.09%)	⬆️

[CodeBlanch]

Relates to #1294