Support go.schedule.duration runtime metric

[dashpole]

Problem Statement

We would like to support the go schedule duration:
https://github.com/open-telemetry/semantic-conventions/blob/main/docs/runtime/go-metrics.md#metric-goscheduleduration

From golang/go#67120:

Rationale: This metric is a measure of scheduling latency that is useful as a fine-grained proxy for overall system load. For example, diffing the distribution over short time windows can provide visibility into the latency impact of uneven load. This metric is battle-tested and has been found to be useful in a variety of scenarios.

However, this has a few challenges:

• The go runtime histogram type doesn't have a sum: https://pkg.go.dev/runtime/metrics#Float64Histogram. It only has buckets and counts. The sum is a critical part of the histogram, as it allows computing averages.
• The go runtime histogram is pre-computed. This means we can't add this histogram using the OTel api. Instead, we will need to model this as a metric.Producer.

[dashpole]

For now, we could use the same approach as https://github.com/prometheus/client_golang/blob/46f77a97fa1e83e7285634745bd5c92c11bf20c7/prometheus/go_collector_latest.go#L541, and estimate the sum.