Explore expanding Account JetStream Statistics for parity with prometheus-nats-exporter

[caleblloyd]

Explore expanding Account JetStream Statistics for parity with prometheus-nats-exporter:

https://github.com/nats-io/prometheus-nats-exporter/blob/f6cb9e62471baa3a74dd048ed320898ce7cd85d1/collector/jsz.go#L33-L57

One concern to evaluate: will adding statistics with labels at the Stream and Consumer level create a potentially high number of Time Series that could affect Prometheus due to high label cardinality - see this cloudflare blog post

[mtmk]

• JetStream server stats: Add JetStream server stats #227
• Stream stats: TODO
• Consumer stats: TODO

[mtmk]

One concern to evaluate: will adding statistics with labels at the Stream and Consumer level create a potentially high number of Time Series that could affect Prometheus due to high label cardinality - see this cloudflare blog post

if this could create an issue for an existing deployment upgrading and creating problems with prometheus then I propose to introduce a couple of flags defaulting to off for stream and consumer stats.