Migrate ZPagesExporter to BatchExportActivityProcessor

[eddynaka]

Related to #1078.

Changes

Please provide a brief description of the changes here. Update the
CHANGELOG.md for non-trivial changes.

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

• Design discussion issue #
• Changes in public API reviewed

[codecov]

Codecov Report

Merging #1108 into master will increase coverage by 1.59%.
The diff coverage is 66.66%.

@@            Coverage Diff             @@
##           master    #1108      +/-   ##
==========================================
+ Coverage   76.01%   77.60%   +1.59%     
==========================================
  Files         223      222       -1     
  Lines        6383     6248     -135     
==========================================
- Hits         4852     4849       -3     
+ Misses       1531     1399     -132     

Impacted Files	Coverage Δ
...rc/OpenTelemetry.Exporter.ZPages/ZPagesExporter.cs	90.90% <0.00%> (-9.10%)	⬇️
...y.Exporter.ZPages/ZPagesExporterStatsHttpServer.cs	91.76% <ø> (+91.76%)	⬆️
...c/OpenTelemetry.Exporter.ZPages/ZPagesProcessor.cs	90.90% <ø> (-0.21%)	⬇️
...metry.Exporter.Zipkin/Implementation/ZipkinSpan.cs	84.88% <46.15%> (-2.93%)	⬇️
...ter.ZPages/Implementation/ZPagesActivityTracker.cs	100.00% <100.00%> (+26.92%)	⬆️
....Exporter.ZPages/ZPagesExporterHelperExtensions.cs	100.00% <100.00%> (ø)
src/OpenTelemetry/Trace/ActivityProcessor.cs	63.15% <0.00%> (-5.27%)	⬇️
...nTelemetry/Internal/OpenTelemetrySdkEventSource.cs	79.41% <0.00%> (-2.95%)	⬇️
src/OpenTelemetry/Trace/ActivitySourceAdapter.cs	91.22% <0.00%> (+3.50%)	⬆️
...ZPages/Implementation/ZPagesExporterEventSource.cs	62.50% <0.00%> (+18.75%)	⬆️
... and 5 more

[cijothomas]

@eddynaka can you rsolve conflict?

[eddynaka]

@eddynaka can you rsolve conflict?

yes, give me some minutes!

[eddynaka]

@eddynaka can you rsolve conflict?

just updated! CI running!