Export metrics for a number of daily users (dau)

[andrii-korotkov-verkada]

Summary

Export a metric about how many distinct users of ArgoCD server were there in the last 24 hours (or maybe support a few other intervals).

Motivation

This can be great to evaluate how many people need to use the tool. It can be interpreted both ways - lower metric can also mean people don't have many issues and rely on autosync.

Proposal

Keep some counter with a rolling window on ArgoCD server and populate daily users from it.