Upgrade metrics and metrics-util crates

[bruceg]

Upgrade metrics >= 0.18 and metrics-util >= 0.12 crates to bring in support for metric handles and a more customizable Registry

This is required due to the introduction of "metric handles" and the more flexible Registry/Storage primitives, which will allow us to interact with the metric values such that we can mutate them rather than simply observe them.

One main thing we'll want to pay attention to is the change, if any, in performance. The changes in metrics-0.18.x were designed to be primarily beneficial to static metric keys, and those who could utilize metric handles directly, both of which we currently do not and cannot do.

This would likely mean some potential performance regressions in areas where we emit many metrics, or emit metrics tied to the rate of events flowing through the topology or specific component.

We've handled these types of issues before by doing local aggregation or some other change to reduce the impact, but this would be at a high level across all metrics that we currently emit, so we'd want to pay attention to changes i.e. as surfaced by soak tests, etc.