Problem Statement

open-telemetry/opentelemetry-specification#2951 defined an experimental MetricProducer interface, which can be used to support metric bridges. Note that the specifications are experimental, so it isn't critical that it is implemented at this time.

Changes:

• Define a MetricProducer interface, following https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/metrics/sdk.md#metricproducer
• Define a RegisterProducer(metricProducer) function on MetricReader, following https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/metrics/sdk.md#registerproducermetricproducer