Add alternatives to the system_networkState RPC query

[tomaka]

It's always been in a kind-of-deprecated-not-supposed-to-be-stable state.
With the new version of libp2p, its output doesn't necessarily make sense anymore (nodes can be connected multiple times), and we would need to change it. Maybe now is the right time to remove this method.

However we first need to add replacements for:

• Getting the local PeerId.
• Getting the local listened multiaddresses.
• more?

[mxinden]

I mentioned in Riot that some Prometheus exporters may use this endpoint. I checked the dot exporter and the substrate telemetry exporter which are all the ones I am aware of. None of them seem to be using the endpoint.

[fgimenez]

We use it in polkadot-secure-validator for getting the peer ids and setting up sentries and validator's multiaddresses, is it possible to get this information elsewhere?

This is the relevant part of the code https://github.com/w3f/polkadot-secure-validator/blob/master/ansible/roles/polkadot-common/tasks/main.yml#L70-L84

[tomaka]

Update: since the RPC query shows up in polkadot-js people have been using it to get a broad overview.

Considering how unstable it is, I'd still be in favour of renaming this RPC to something else and adding alternatives so that it doesn't get used by scripts.