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/policy.rs

@@ -21,13 +21,7 @@
 //! Contains a `DenyUnsafe` type that can be used to deny potentially unsafe
 //! RPC when accessed externally.
 
-use jsonrpsee::{
-	core::Error as JsonRpseeError,
-	types::{
-		error::{CallError, ErrorCode},
-		ErrorObject,
-	},
-};
+use jsonrpsee::types::{error::ErrorCode, ErrorObject, ErrorObjectOwned};
 
 /// Signifies whether a potentially unsafe RPC should be denied.
 #[derive(Clone, Copy, Debug)]
@@ -61,18 +55,8 @@ impl std::fmt::Display for UnsafeRpcError {
 
 impl std::error::Error for UnsafeRpcError {}
 
-impl From<UnsafeRpcError> for CallError {
-	fn from(e: UnsafeRpcError) -> CallError {
-		CallError::Custom(ErrorObject::owned(
-			ErrorCode::MethodNotFound.code(),
-			e.to_string(),
-			None::<()>,
-		))
-	}
-}
-
-impl From<UnsafeRpcError> for JsonRpseeError {
-	fn from(e: UnsafeRpcError) -> JsonRpseeError {
-		JsonRpseeError::Call(e.into())
+impl From<UnsafeRpcError> for ErrorObjectOwned {
+	fn from(e: UnsafeRpcError) -> ErrorObjectOwned {
+		ErrorObject::owned(ErrorCode::MethodNotFound.code(), e.to_string(), None::<()>)
 	}
 }