Exporter/OcAgent: Skeleton and workflow for worker thread.

[songy23]

Split from #1492.

Updates #1408.

[codecov-io]

Codecov Report

Merging #1574 into master will decrease coverage by 0.45%.
The diff coverage is 0%.

@@             Coverage Diff              @@
##             master    #1574      +/-   ##
============================================
- Coverage     83.47%   83.01%   -0.46%     
+ Complexity     1813     1732      -81     
============================================
  Files           261      258       -3     
  Lines          8339     7978     -361     
  Branches        803      766      -37     
============================================
- Hits           6961     6623     -338     
+ Misses         1123     1120       -3     
+ Partials        255      235      -20

Impacted Files	Coverage Δ	Complexity Δ
...e/ocagent/OcAgentTraceServiceConnectionWorker.java	0% <0%> (ø)	0 <0> (?)
...java/io/opencensus/contrib/http/HttpExtractor.java	0% <0%> (-100%)	0% <0%> (-1%)
...census/trace/propagation/PropagationComponent.java	80% <0%> (-20%)	3% <0%> (ø)
...monitoredresource/util/MonitoredResourceUtils.java	14.28% <0%> (-16.97%)	1% <0%> (-1%)
...sus/implcore/trace/export/ExportComponentImpl.java	85% <0%> (-15%)	9% <0%> (-1%)
.../opencensus/impl/internal/DisruptorEventQueue.java	79.54% <0%> (-11.37%)	5% <0%> (-1%)
...rter/stats/stackdriver/StackdriverExportUtils.java	79.06% <0%> (-10.94%)	37% <0%> (-12%)
...src/main/java/io/opencensus/resource/Resource.java	82.75% <0%> (-8.36%)	14% <0%> (-8%)
...io/opencensus/contrib/zpages/ZPageHttpHandler.java	37.5% <0%> (-7.67%)	5% <0%> (ø)
...er/stats/stackdriver/StackdriverStatsExporter.java	66.66% <0%> (-4.59%)	12% <0%> (-2%)
... and 32 more

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[songy23]

Friendly ping. I think we need to agree on the workflow before I move on to implementation.

[songy23]

PTAL.

[bogdandrutu]

Skeleton looks good.

[songy23]

Thanks!