rpc: backpressured RPC server (bump jsonrpsee 0.20) (#1313)

This is a rather big change in jsonrpsee, the major things in this bump
are:
- Server backpressure (the subscription impls are modified to deal with
that)
- Allow custom error types / return types (remove jsonrpsee::core::Error
and jsonrpee::core::CallError)
- Bug fixes (graceful shutdown in particular not used by substrate
anyway)
   - Less dependencies for the clients in particular
   - Return type requires Clone in method call responses
   - Moved to tokio channels
   - Async subscription API (not used in this PR)

Major changes in this PR:
- The subscriptions are now bounded and if subscription can't keep up
with the server it is dropped
- CLI: add parameter to configure the jsonrpc server bounded message
buffer (default is 64)
- Add our own subscription helper to deal with the unbounded streams in
substrate

The most important things in this PR to review is the added helpers
functions in `substrate/client/rpc/src/utils.rs` and the rest is pretty
much chore.

Regarding the "bounded buffer limit" it may cause the server to handle
the JSON-RPC calls
slower than before.

The message size limit is bounded by "--rpc-response-size" thus "by
default 10MB * 64 = 640MB"
but the subscription message size is not covered by this limit and could
be capped as well.

Hopefully the last release prior to 1.0, sorry in advance for a big PR

Previous attempt: https://github.com/paritytech/substrate/pull/13992

Resolves https://github.com/paritytech/polkadot-sdk/issues/748, resolves
https://github.com/paritytech/polkadot-sdk/issues/627

substrate/client/rpc-api/src/mixnet/error.rs

@@ -18,7 +18,7 @@
 
 //! Mixnet RPC module errors.
 
-use jsonrpsee::types::error::{CallError, ErrorObject};
+use jsonrpsee::types::error::{ErrorObject, ErrorObjectOwned};
 use sc_mixnet::{PostErr, RemoteErr, TopologyErr};
 
 /// Mixnet RPC error type.
@@ -27,7 +27,7 @@ pub struct Error(pub sc_mixnet::Error);
 /// Base code for all mixnet errors.
 const BASE_ERROR: i32 = crate::error::base::MIXNET;
 
-impl From<Error> for jsonrpsee::core::Error {
+impl From<Error> for ErrorObjectOwned {
 	fn from(err: Error) -> Self {
 		let code = match err.0 {
 			sc_mixnet::Error::ServiceUnavailable => BASE_ERROR + 1,
@@ -43,6 +43,6 @@ impl From<Error> for jsonrpsee::core::Error {
 			sc_mixnet::Error::Remote(RemoteErr::Other(_)) => BASE_ERROR + 200,
 			sc_mixnet::Error::Remote(RemoteErr::Decode(_)) => BASE_ERROR + 201,
 		};
-		CallError::Custom(ErrorObject::owned(code, err.0.to_string(), None::<()>)).into()
+		ErrorObject::owned(code, err.0.to_string(), None::<()>)
 	}
 }