* Add Prometheus stats for admin count
Fixes#20828
Reports time series for admin count. Counts are separated by state (active, AFK, or deadminned) and admin rank.
* Use static constructor instead of static readonly for the metric
Docs recommend this due to inconsistent execution of C# static constructors.
* Remove static usage, use IoC IMeterFactory.
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Co-authored-by: metalgearsloth <comedian_vs_clown@hotmail.com>
