schedulerlatency: Increase the go scheduler latency metric time coverage

[iskettaneh]

Before this commit, the go scheduler latency metric was publish once every 10 seconds, and it was based on 2.5 seconds worth of data. That meant that there was 75% blind spot in that metric. This is especially important for short-lived overload that might not have been detected with this metric.

This commit builds on the current interval at which we measure the scheduler latency (100ms), and keeps adding these 100ms measurements into a histogram that gets published (and cleared) every 10s.

The figure below shows the Before/After metric on 2 clusters with the old and the new metric when running the following command: while true; do timeout 3.5 roachprod run $CLUSTER:4 -- './cockroach workload run kv --concurrency=256 --read-percent=95 --duration=120m {pgurl:1}'; sleep 57.5; done

You can see that in the Before figure, many of these spikes are missed. While they are visible in the new metric.

Release note: None

Fixes: #158475

[blathers-crl]

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[cockroach-teamcity]

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