Add Node Telemetry details

[zhyatt]

RPC command additions and other details to help make telemetry useful (response definitions?)

Related to: nanocurrency/nano-node#2446 and nanocurrency/nano-node#2521

[zhyatt]

Also related: nanocurrency/nano-node#2522 and nanocurrency/nano-node#2524

[wezrule]

Also: nanocurrency/nano-node#2560

[wezrule]

Done in #231

[wezrule]

Also needs: nanocurrency/nano-node#2634 & nanocurrency/nano-node#2618

[wezrule]

And nanocurrency/nano-node#2728

[zhyatt]

@wezrule Can you verify the published telemetry details across RPC and WebSocket responses? It seems like active_difficulty, address and port are inconsistent between the two.

[wezrule]

@zhyatt active_difficulty was missing from websocket, good catch! address & port are always in websocket, but only in RPC when raw is set to true. Another possible inconsistency though is that websocket "topic" uses telemetry while RPC uses node_telemetry, hmm, would it make sense if they were the same?

[zhyatt]

@wezrule Thanks for updating. I think consistency would be good here. Perhaps an update on the websocket topic to be node_telemetry to be more explicit would make sense.

[zhyatt]

Updating all internally to use just telemetry while sometimes referred to as "node telemetry" in communications and such. Related #322 and nanocurrency/nano-node#2804