add commands to monitor NATS Streaming

[NATS Streaming has a monitoring API](https://docs.nats.io/nats-streaming-concepts/monitoring/endpoints) that we can use.

Start with the linked NATS Streaming monitoring API documentation, then inspect the repository's existing publish and subscribe command entry points. Determine which monitoring commands and API responses belong in the CLI; done means the supported monitoring operations are exposed consistently and their behavior is covered by the project's available checks.

Written by the indexing model from the issue text.