Add dispatch cycle duration metric for flow control

[RyanRosario]

kind/feature

What this PR does / why we need it:

Adds a metric that computes that length of time, in nanoseconds, that each dispatch cycle took. This is useful for measuring performance of new algorithms.

Related to #1708

Does this PR introduce a user-facing change?:

NO

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[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: RyanRosario
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[k8s-ci-robot]

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