Currently the OpenTelemetryMetricsBackend reports a number of metrics, following the naming conventions of OpenTelemetry.

However, we only report raw metric values, without any of the attributes as defined here.

The goal of this issue is to report the metrics along with the required attributes. Optionally, we might include other attributes, if this is feasible and "makes sense".

The abstractions currently present in OpenTelemetryMetricsBackend might need updating/extending/refactoring; since this targets version 4 (yet unreleased), there are no compatibility requirements.