metrics: add IOMetrics

[iRevive]

The functionality relies on the cats-effect MBeans to collect metrics. There are three different metrics:

1) Compute

Available via IOMetrics.registerComputeMetrics:

• cats.effect.runtime.compute.thread.count
• cats.effect.runtime.compute.thread.active.count
• cats.effect.runtime.compute.thread.blocked.count
• cats.effect.runtime.compute.thread.searching.count
• cats.effect.runtime.compute.fiber.enqueued.count

2) CPU starvation

Available via IOMetrics.registerCpuStarvationMetrics:

• cats.effect.runtime.cpu.starvation.count
• cats.effect.runtime.cpu.starvation.clock.drift.current
• cats.effect.runtime.cpu.starvation.clock.drift.max

3) Local queue

Available via IOMetrics.registerLocalQueueMetrics:

• cats.effect.runtime.local.queue.fiber.enqueued.count
• cats.effect.runtime.local.queue.fiber.spillover.count
• cats.effect.runtime.local.queue.fiber.steal.attempt.count
• cats.effect.runtime.local.queue.fiber.stolen.count
• cats.effect.runtime.local.queue.fiber.total.count
• cats.effect.runtime.local.queue.head.index
• cats.effect.runtime.local.queue.tag.head.real
• cats.effect.runtime.local.queue.tag.head.steal
• cats.effect.runtime.local.queue.tag.tail
• cats.effect.runtime.local.queue.tail.index

Here, I'm a bit skeptical about whether the following metrics are relevant at all:

• cats.effect.runtime.local.queue.head.index
• cats.effect.runtime.local.queue.tag.head.real
• cats.effect.runtime.local.queue.tag.head.steal
• cats.effect.runtime.local.queue.tag.tail
• cats.effect.runtime.local.queue.tail.index

[swapdonkey]

Looks good.
I think your right to skip:
cats.effect.runtime.local.queue.head.index
cats.effect.runtime.local.queue.tag.head.real
cats.effect.runtime.local.queue.tag.head.steal
cats.effect.runtime.local.queue.tag.tail
cats.effect.runtime.local.queue.tail.index

I think they'll just be noise