Add way to query back reserved nodes through JSON-RPC layer

[tomaka]

Apparently some users want to be able to query back the reserved nodes that they passed through --reserved-nodes and added/removed through addReservedPeer and removeReservedPeer.

[h4x3rotab]

Indeed! Recently we are building a Substrate validator DevOps framework. We use addReservedPeer and removeReservedPeer to pair our nodes in the private network in a cluster, but there's no way to query the current reserved node list. It would be very useful.

Also chatted with @wpank about this idea. Quoted here:

There's the system_networkState call, which dumps a lot of networking info about the state of the network from the nodes point of view, and then the system_peers rpc call, which shows the current peers the node is connected to. I imagine the reserved status can probably be added to the system_peers rpc call as a bool - something like reservedPeer: true or something like that. If this is a feature that would be really useful, best to add an issue to substrate

[tomaka]

system_reservedPeers 🚀