calculating consul.runtime.total_gc_pause_ns

#### Overview of the Issue

I don't understand the calculation here. If this is a cumulative number, "since Consul started", how can "the value return is more than ..." be possible? It'll always be high, since it accumulates. How do you calculate GC?

> https://developer.hashicorp.com/consul/tutorials/day-2-operations/monitor-datacenter-health#garbage-collection

>If the value return is more than 2 seconds/minute, you should start investigating the cause. If it exceeds 5 seconds per minute, >you should consider the datacenter to be in a critical state and start ensuring failure recovery procedures are up-to-date and >start investigating. Below is an example of healthy GC pause.

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#### Reproduction Steps
```
# curl -s http://127.0.0.1:8500/v1/agent/metrics | jq . | grep -A3 consul.runtime.total_gc_pause_ns
"Name": "consul.runtime.total_gc_pause_ns",
"Value": 568344960,
"Labels": {}
},
```