ctl: option to group and configure rpc endpoints to watch

[Arqu]

I'm looking into leveraging iroh-ctl as a hub to report on some stats, for that it would be ideal if I could list and tag different RpcClientConfig so that it watches over all of them. Ideally I could do aggregate result vs per tag/namespace/somekey.

ie iroh-ctl status --watch --cfg=./mycfg.[toml|yaml|json] & iroh-ctl status --watch --tag=node_omega --cfg=./mycfg.[toml|yaml|json]

If we had this, I'd be happy to add an option to run --with-metrics so that it reports some sort of uptime metric. Useful for a central health/uptime monitoring solution.