Clean up metric reader options

[alanwest]

• Removes MetricReaderType enumeration.
• Adds PeriodicExportingMetricReaderOptions.ExportTimeoutMilliseconds with a default of 30000 for all push exporters.
• MetricReaderOptions.PeriodicExportingMetricReaderOptions is no longer settable.

[codecov]

Codecov Report

Merging #3038 (21798c0) into main (0254d34) will increase coverage by 0.16%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #3038      +/-   ##
==========================================
+ Coverage   84.74%   84.91%   +0.16%     
==========================================
  Files         258      259       +1     
  Lines        9105     9112       +7     
==========================================
+ Hits         7716     7737      +21     
+ Misses       1389     1375      -14     

Impacted Files	Coverage Δ
...rter.InMemory/InMemoryExporterMetricsExtensions.cs	66.66% <100.00%> (-1.34%)	⬇️
...nTelemetryProtocol/OtlpMetricExporterExtensions.cs	70.37% <100.00%> (-1.06%)	⬇️
...ry/Internal/PeriodicExportingMetricReaderHelper.cs	100.00% <100.00%> (ø)
src/OpenTelemetry/Metrics/MetricReaderOptions.cs	100.00% <100.00%> (ø)
...Telemetry/Metrics/PeriodicExportingMetricReader.cs	76.47% <100.00%> (ø)
...ry/Metrics/PeriodicExportingMetricReaderOptions.cs	100.00% <100.00%> (ø)
...heus/Implementation/PrometheusCollectionManager.cs	79.74% <0.00%> (-2.54%)	⬇️
...metryProtocol/Implementation/ActivityExtensions.cs	90.41% <0.00%> (+3.65%)	⬆️
...xporter.OpenTelemetryProtocol/OtlpTraceExporter.cs	77.27% <0.00%> (+18.18%)	⬆️
...entation/ExportClient/OtlpGrpcTraceExportClient.cs	78.57% <0.00%> (+28.57%)	⬆️

[reyang]

Do we need timeout 30000 or Infinite?

[alanwest]

I just submitted open-telemetry/opentelemetry-specification#2415 for further clarification.

I'll set to Infinite for now and change depending on how things shake out.

[reyang]

Do we need timeout 30000 or Infinite?

[cijothomas]

LGTM except the same qn as Reiley about default for ExportTimeout to be infinite vs 30

[utpilla]

We could get rid of the default exportInterval and timeout in PeriodicExportingMetricReader now as we would always be providing the parameter values for the PeriodicExportingMetricReader ctor:
https://github.com/open-telemetry/opentelemetry-dotnet/blob/main/src/OpenTelemetry/Metrics/PeriodicExportingMetricReader.cs#L31-L32

[alanwest]

We could get rid of the default exportInterval and timeout in PeriodicExportingMetricReader now as we would always be providing the parameter values for the PeriodicExportingMetricReader ctor:

It is still possible to instantiate the PeriodicExportingMetricReader by itself, so the defaults are still relevant. Something like

var metricExporter = new ConsoleExporter();
var metricReader = new PeriodicExportingMetricReader(exporter);
var meterProviderBuilder = Sdk.CreateMeterProviderBuilder().AddReader(metricReader);