Add a way to customize `SubscriptionId` generation

[librelois]

I started to migrate the codebase of frontier on jsonrpsee based on the branch polkadot-jsonrpsee-v0.9.13 and I notice that jsonrpsee lacks an essential feature that makes it impossible to use it in frontier: the possibility to customize the way to generate SubscriptionId.

Indeed, frontier must reproduce the ethereum RPC api with accuracy, this includes providing SubscriptionId in string form with 16 bytes in hexadecimal representation prefixed by "0x".

Frontier currently uses jsonrpc, which allows custom generation of subscription ids with the with_id_provider function: https://github.com/paritytech/jsonrpc/blob/609d7a6cc160742d035510fa89fb424ccf077660/pubsub/src/manager.rs#L154

[niklasad1]

fair enough then, we should support this.

//cc @maciejhirsz

Should we simply have another param to register_subscription that takes a closure -> Into<SubscriptionId>?
However, it will be hard to solve "nicely" in the proc macro definition... I guess

Thoughts?

[maciejhirsz]

Do we need to touch proc macros with this? I'd think this is more of a server config stuff. And yeah, a closure (generator) that yields a new SubscriptionId should suffice.

[niklasad1]

SubscriptionId generator is in the RpcModule so it's not possible to make this configuration based on the server itself. However, we could include it the callback closure similar to what we did for MaxPayloadSize a.k.a MethodSink that should work then no proc macro stuff needs changing....

any other ideas?

[niklasad1]

Closed by #604