Zipkin Span tags will no longer be populated with Resource Attributes

[Austin-Tan]

Fixes #1656.

Changes

Please provide a brief description of the changes here.

For significant contributions please make sure you have completed the following items:

• CHANGELOG.md updated for non-trivial changes
• Design discussion issue #
• Changes in public API reviewed

[codecov]

Codecov Report

Merging #1663 (a8a5fb8) into master (842daff) will decrease coverage by 0.04%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #1663      +/-   ##
==========================================
- Coverage   82.17%   82.13%   -0.05%     
==========================================
  Files         250      250              
  Lines        6767     6763       -4     
==========================================
- Hits         5561     5555       -6     
- Misses       1206     1208       +2     

Impacted Files	Coverage Δ
...rc/OpenTelemetry.Exporter.Zipkin/ZipkinExporter.cs	87.50% <100.00%> (-0.55%)	⬇️
...emetry.Api/Internal/OpenTelemetryApiEventSource.cs	76.47% <0.00%> (-5.89%)	⬇️
...metry.Exporter.Zipkin/Implementation/ZipkinSpan.cs	94.50% <0.00%> (-1.10%)	⬇️
...Telemetry/Internal/SelfDiagnosticsEventListener.cs	94.28% <0.00%> (+1.42%)	⬆️

[cijothomas]

More changes are needed in light of recent spec changes about default resource. But that can be separate PRs.