Migrate JaegerExporter 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

[reyang]

LGTM.

[codecov]

Codecov Report

Merging #1125 into master will decrease coverage by 0.23%.
The diff coverage is 11.11%.

@@            Coverage Diff             @@
##           master    #1125      +/-   ##
==========================================
- Coverage   77.57%   77.33%   -0.24%     
==========================================
  Files         222      222              
  Lines        6282     6284       +2     
==========================================
- Hits         4873     4860      -13     
- Misses       1409     1424      +15     

Impacted Files	Coverage Δ
...rc/OpenTelemetry.Exporter.Jaeger/JaegerExporter.cs	69.76% <0.00%> (-20.48%)	⬇️
....Exporter.Jaeger/JaegerExporterHelperExtensions.cs	100.00% <100.00%> (ø)
...Exporter.Jaeger/Implementation/JaegerUdpBatcher.cs	86.33% <0.00%> (-5.04%)	⬇️
...us/Implementation/PrometheusExporterEventSource.cs	72.72% <0.00%> (+9.09%)	⬆️