Expose code intel usage stats via updatecheck
Created by: efritz
Expose the data from GetCodeIntelUsageStatistics
via updatecheck requests.
This does expose user counts and event latencies, but does not expose event counts yet. We'll be adding an opt-out site admin flag to disable event counts in https://github.com/sourcegraph/sourcegraph/pull/8140, at which point they will be sent by default.