Add example crate for custom rlpx subprotocol

[mattsse]

Describe the feature

Add a new example that showcases rlpx subprotocols, similar to this simple Ping/Pong protocol

reth/crates/net/network/tests/it/multiplex.rs

Lines 25 to 26 in c9c269b

	/// A simple Rplx subprotocol for
	mod proto {

but something more sophisticated

A protocol can be installed via:

reth/crates/net/network/src/network.rs

Lines 210 to 214 in c9c269b

	impl NetworkProtocols for NetworkHandle {
	fn add_rlpx_sub_protocol(&self, protocol: RlpxSubProtocol) {
	self.send_message(NetworkHandleMessage::AddRlpxSubProtocol(protocol))
	}
	}

Additional context

No response

[owanikin]

Hi @mattsse can I work on this?

[mattsse]

assigned, lmk if you need pointers/ have questions

[owanikin]

Thank you! Yeah, lol I need all the pointers I can get. You can give as many as you think will be useful.

[mattsse]

we want a new example crate, similar to this setup:

reth/examples/custom-inspector/src/main.rs

Lines 33 to 38 in 520d635

	fn main() {
	Cli::<RethCliTxpoolExt>::parse()
	.run(|builder, args| async move {
	// launch the node
	let NodeHandle { mut node, node_exit_future } =
	builder.node(EthereumNode::default()).launch().await?;

and after launch we inject a new rlpx protocol handler via the network node.network

the rlpx can be similar to the test example, could even be something like simple string message exchange

[JackG-eth]

Happy to take ownership of this issue

[owanikin]

@JackG-eth Please this is mine, working on it.

[onbjerg]

@owanikin Hey, what's the status of this? Feel free to open a draft PR if you need feedback/direction or you are stuck :)

[owanikin]

@onbjerg I was stuck for a while :( .Kindly give me until the end of the week to make a PR. Thank you :)

[rupam-04]

@mattsse How will things change for the NodeHandle struct in PR #8017 as here we are working with the NetworkHandle struct? Any pointers on that?

[mattsse]

this shouldn't require any changes to the NodeHandle struct, instead the rlpx protocol can be installed via the NetworkHandle

[shekhirin]

@loocapro are you going to take this?

[loocapro]

@loocapro are you going to take this?

Yess!