[sdk-node] implement enviornment configuration for auto-paired PeriodicExportingMetricReader

[pichlermarc]

Description

The specification defines that PeriodicExporingMetricReaders that are auto-paired with an exporter can be configured via environment variables.

For this issue to be considered done we need to:

• implement [sdk-node] automatically configure metrics exporter based on enviornment variables #4551
• in @opentelmetry/sdk-node, where the automatic pairing from [sdk-node] automatically configure metrics exporter based on enviornment variables #4551 is implemented, read the env vars from OTEL_METRIC_EXPORT_INTERVAL/OTEL_METRIC_EXPORT_TIMEOUT and configure the auto-paired PeriodicExportingMetricReader accordingly. Use defaults if the env vars are unset.

Additional infomation

Original feature-request:

• Implement Periodic exporting MetricReader environment variables #4562

[aabmass]

The specification defines that PeriodicExporingMetricReaders that are auto-paired with an exporter can be configured via environment variables.

Does the spec actually say anything about this only applying when auto-paired? The BatchSpanProcessor reads from the environment variables directly

opentelemetry-js/packages/opentelemetry-sdk-trace-base/src/export/BatchSpanProcessorBase.ts

Lines 55 to 58 in 31eb60d

	this._maxExportBatchSize =
	typeof config?.maxExportBatchSize === 'number'
	? config.maxExportBatchSize
	: env.OTEL_BSP_MAX_EXPORT_BATCH_SIZE;

so the environment variables are applied globally. I'm guessing this is related to the yaml config file conversation and the related concern around precedence