Add unstable JSON-RPC function that exports recent networking events

[tomaka]

paritytech/smoldot#2245

[tomaka]

This function should be added as a PR to https://github.com/paritytech/json-rpc-interface-spec/

[tomaka]

cc paritytech/json-rpc-interface-spec#91

[tomaka]

We need to add a few events in established.rs:

• When a notifications out request has successfully negotiated the substream.
• When a request has successfully negotiated the substream.
• When we open or close a ping substream.
• When the remote opens or closes a ping substream.

All the JSON-RPC events can then be derived from this.

Then, the events service.rs need to be updated as well. This part is unfortunately not completely clear to me.

[tomaka]

When a notifications out request has successfully negotiated the substream.
When a request has successfully negotiated the substream.

Actually, we can just pretend that the substream has opened when we start the opening, so there's no need for these two events.

[tomaka]

Then, the events service.rs need to be updated as well. This part is unfortunately not completely clear to me.

The solution (which I feel stupid for not thinking of earlier) is to provide an OpaqueEvent which can be turned into either a LowLevelEvent or an optional HighLevelEvent.

[tomaka]

A big difficulty, which I didn't anticipate, is that the connections that the network service opens do not target a chain in particular, but the JSON-RPC function does target a specific chain.

This means that we have to somehow report to the API user only connections that we think might belong to a specific chain. Reporting only some connections might be misleading? Maybe we should report all connections?