Added ServiceName option to OtlpExporter

[CodeBlanch]

Fixes #1416

Changes

Add ServiceName option to OtlpExporter to bring it into parity with Zipkin & Jaeger.

TODOs:

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

[codecov]

Codecov Report

Merging #1420 into master will increase coverage by 0.56%.
The diff coverage is 67.50%.

@@            Coverage Diff             @@
##           master    #1420      +/-   ##
==========================================
+ Coverage   81.31%   81.87%   +0.56%     
==========================================
  Files         227      227              
  Lines        6117     6086      -31     
==========================================
+ Hits         4974     4983       +9     
+ Misses       1143     1103      -40     

Impacted Files	Coverage Δ
...metryProtocol/Implementation/ActivityExtensions.cs	86.89% <47.36%> (+13.06%)	⬆️
...try.Exporter.OpenTelemetryProtocol/OtlpExporter.cs	58.97% <85.00%> (+30.40%)	⬆️
...orter.OpenTelemetryProtocol/OtlpExporterOptions.cs	100.00% <100.00%> (ø)
...ZPages/Implementation/ZPagesExporterEventSource.cs	56.25% <0.00%> (-6.25%)	⬇️
....Prometheus/PrometheusExporterMetricsHttpServer.cs	74.50% <0.00%> (-1.97%)	⬇️

[CodeBlanch]

@eddynaka @cijothomas Would you guys mind taking another look at this? In order to make the tests work I had to switch the resource from a static on ActivityExtensions to a field on OtlpExporter.

[eddynaka]

@eddynaka @cijothomas Would you guys mind taking another look at this? In order to make the tests work I had to switch the resource from a static on ActivityExtensions to a field on OtlpExporter.

@CodeBlanch , took a look. Looks fine. Don't think that will affect performance/allocation much.
Very nice.