In case of MQTT with lots of clients，decrease metrics number for consumer.

[ianzhang1988]

If there are a million MQTT clients, They would produce a huge number of promethus entries as jetstream consumers. This could put presure on promethus servser. And hard to make sence.

I think seperate MQTT consumsers from consumers from other stream would be nice. Something like:

1. Summary MQTT status: total consumer num, total num delivered, etc.
2. Top N consumers have outstanding numbers like pending msgs.