Add Index usage metrics to serverStatus

Summary

Define and add new metrics to serverStatus in order to better track index usage.

Motivation

In order to make more informed Product decisions and expand the data we consume to better support customers feature requests and issue triage we need to continue to build out better telemetry around usage. By adding metrics to track index usage and behavior we will be able to not only measure the success of features and inits, but better understand how to develop and prioritize new features related to indexing and improve diagnostic capability. 

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