[sdk-node] automatically configure logs exporter based on enviornment variables

[pichlermarc]

Currently, we don't auto-configure a LogRecordProcessor/exporter combination when using the @opentelemetry/sdk-node package.
Goal of this issue is to implement exporter selection for metrics based on this specification:

• https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/configuration/sdk-environment-variables.md#exporter-selection

For this issue to be considered done we need to implement the following behavior:

If no log record proccessor is configured by the user:

• use OTEL_LOGS_EXPORTER environment variable to determine an exporter and add it to the LoggerProvider that's created by NodeSDK
  • pair it up with a BatchLogRecordProcessor
  • see https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/configuration/sdk-environment-variables.md#exporter-selection
• use the OTEL_EXPORTER_OTLP_LOGS_PROTOCOL to determine the OTLP exporter to use (http/json, http/protobuf, grpc)
  • see https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/protocol/exporter.md#specify-protocol
• use the OTEL_EXPORTER_OTLP_PROTOCOL env var as a fallback to the above to determine the OTLP exporter to use (http/json, http/protobuf, grpc)
• fallback to using http/protobuf if none of the two protocol env vars are set

[mhennoch]

Can assign to me.

[pichlermarc]

It's yours 🙂