Exporting tags consistently

[alanwest]

#3262 standardized how we handle tags in the OTLP exporter for traces, metrics, and logs.

I have generalized that work in a way to get code reuse across for the Zipkin and Jaeger exporters. I suspect this could be used for Prometheus too, but haven't touched Prometheus in this PR.

This PR will also address a number of bugs:

• fixes process.command_args serializes as System.String[] #3229
• Array values are not handled correctly in the Jaeger and Zipkin exporters. Per the spec:

  Array values MUST be serialized to string like a JSON list...

[reyang]

+1 like the idea!

[codecov]

Codecov Report

Merging #3281 (5fa4281) into main (b9839f6) will increase coverage by 0.00%.
The diff coverage is 92.98%.

@@           Coverage Diff           @@
##             main    #3281   +/-   ##
=======================================
  Coverage   85.38%   85.39%           
=======================================
  Files         265      269    +4     
  Lines        9541     9552   +11     
=======================================
+ Hits         8147     8157   +10     
- Misses       1394     1395    +1     

Impacted Files	Coverage Δ
...elemetry.Exporter.Jaeger/Implementation/Process.cs	80.48% <ø> (+10.27%)	⬆️
...tation/OpenTelemetryProtocolExporterEventSource.cs	85.00% <ø> (-1.37%)	⬇️
...etryProtocol/Implementation/LogRecordExtensions.cs	87.95% <50.00%> (ø)
...metry.Exporter.Zipkin/Implementation/ZipkinSpan.cs	95.00% <50.00%> (-1.63%)	⬇️
....Jaeger/Implementation/JaegerActivityExtensions.cs	95.62% <85.71%> (-0.79%)	⬇️
...Protocol/Implementation/OtlpKeyValueTransformer.cs	85.71% <85.71%> (ø)
...rter.Jaeger/Implementation/JaegerTagTransformer.cs	100.00% <100.00%> (ø)
...rc/OpenTelemetry.Exporter.Jaeger/JaegerExporter.cs	87.17% <100.00%> (+0.11%)	⬆️
...metryProtocol/Implementation/ActivityExtensions.cs	94.50% <100.00%> (-0.04%)	⬇️
...tryProtocol/Implementation/MetricItemExtensions.cs	93.83% <100.00%> (+0.04%)	⬆️
... and 10 more

[alanwest]

TODO: Gotta figure out a better place to put the shared TagTransformer.cs file.

I think this causes an unnecessary new dependency on the SDK project. Technically this is only required for the shared TagTransformer class which is only used by exporters.

[CodeBlanch]

Could have a dummy project just to house shared stuff like https://github.com/open-telemetry/opentelemetry-dotnet-contrib/tree/main/src/OpenTelemetry.Contrib.Shared 🤷

[alanwest]

I ended up just excluding TagTransformer.cs from compilation. See: 673ade0

I tried the separate project idea and ended up needing to pull in the OpenTelemetrySdkEventSource for logging. Also, a new project may have resulted in a gratuitous nuget package. Both of these concerns could be overcome, so if folks think a separate project is better, I'm happy to go that route.

Nevermind, that caused other problems. I solved this more simply by just moving the code that required System.Text.Json to the projects that actually needed it. 74df0df

[CodeBlanch]

Some nits and suggestions but LGTM.