chore: implement UpdateRates with simple in-memory tracker

[grobinson-grafana]

What this PR does / why we need it:

This commit implements UpdateRates with a simple in-memory tracker. It does not replicate to Kafka currently because this produces a huge amount of volume that we need to replay on every restart. For now, since rate buckets are refilled very quickly, I propose we keep these in-memory without replication while we think about how to solve this.

Which issue(s) this PR fixes:
Fixes #

Special notes for your reviewer:

Checklist

• Reviewed the CONTRIBUTING.md guide (required)
• Documentation added
• Tests updated
• Title matches the required conventional commits format, see here
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