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/system/error.rs

@@ -19,9 +19,9 @@
 //! System RPC module errors.
 
 use crate::system::helpers::Health;
-use jsonrpsee::{
-	core::Error as JsonRpseeError,
-	types::error::{CallError, ErrorObject},
+use jsonrpsee::types::{
+	error::{ErrorCode, ErrorObject},
+	ErrorObjectOwned,
 };
 
 /// System RPC Result type.
@@ -36,6 +36,12 @@ pub enum Error {
 	/// Peer argument is malformatted.
 	#[error("{0}")]
 	MalformattedPeerArg(String),
+	/// Call to an unsafe RPC was denied.
+	#[error(transparent)]
+	UnsafeRpcCalled(#[from] crate::policy::UnsafeRpcError),
+	/// Internal error.
+	#[error("{0}")]
+	Internal(String),
 }
 
 // Base code for all system errors.
@@ -45,17 +51,16 @@ const NOT_HEALTHY_ERROR: i32 = BASE_ERROR + 1;
 // Peer argument is malformatted.
 const MALFORMATTED_PEER_ARG_ERROR: i32 = BASE_ERROR + 2;
 
-impl From<Error> for JsonRpseeError {
-	fn from(e: Error) -> Self {
+impl From<Error> for ErrorObjectOwned {
+	fn from(e: Error) -> ErrorObjectOwned {
 		match e {
 			Error::NotHealthy(ref h) =>
-				CallError::Custom(ErrorObject::owned(NOT_HEALTHY_ERROR, e.to_string(), Some(h))),
-			Error::MalformattedPeerArg(e) => CallError::Custom(ErrorObject::owned(
-				MALFORMATTED_PEER_ARG_ERROR + 2,
-				e,
-				None::<()>,
-			)),
+				ErrorObject::owned(NOT_HEALTHY_ERROR, e.to_string(), Some(h)),
+			Error::MalformattedPeerArg(e) =>
+				ErrorObject::owned(MALFORMATTED_PEER_ARG_ERROR, e, None::<()>),
+			Error::UnsafeRpcCalled(e) => e.into(),
+			Error::Internal(e) =>
+				ErrorObjectOwned::owned(ErrorCode::InternalError.code(), e, None::<()>),
 		}
-		.into()
 	}
 }