OpenTelemetry Protocol (OTLP) MeterRegistry

[shakuzen]

Please describe the feature request.
Use Micrometer to ship metrics in OTLP format for metrics.

Rationale
Some metrics backends and metrics intermediaries like proxies/collectors/daemons that may do some processing of metrics before ingestion will support OpenTelemetry Protocol format. If there is enough interest from users, we should support this use case.

Additional context
This can be separate from a MeterRegistry implementation that delegates to OpenTelemetry metrics API. By focusing on the publishing format, this makes it most similar to other MeterRegistry implementations.

While the rest of the OTel metrics efforts are not stable yet, the OTLP metrics format is marked stable, unblocking this work.

[twicksell]

+1 to this issue, I have this exact problem of needing to interact with a proxy which supports OTLP.