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/src/offchain/tests.rs

@@ -39,7 +39,6 @@ fn local_storage_should_work() {
 
 #[test]
 fn offchain_calls_considered_unsafe() {
-	use jsonrpsee::types::error::CallError;
 	let storage = InMemOffchainStorage::default();
 	let offchain = Offchain::new(storage, DenyUnsafe::Yes);
 	let key = Bytes(b"offchain_storage".to_vec());
@@ -47,14 +46,14 @@ fn offchain_calls_considered_unsafe() {
 
 	assert_matches!(
 		offchain.set_local_storage(StorageKind::PERSISTENT, key.clone(), value.clone()),
-		Err(JsonRpseeError::Call(CallError::Custom(err))) => {
-			assert_eq!(err.message(), "RPC call is unsafe to be called externally")
+		Err(Error::UnsafeRpcCalled(e)) => {
+			assert_eq!(e.to_string(), "RPC call is unsafe to be called externally")
 		}
 	);
 	assert_matches!(
 		offchain.get_local_storage(StorageKind::PERSISTENT, key),
-		Err(JsonRpseeError::Call(CallError::Custom(err))) => {
-			assert_eq!(err.message(), "RPC call is unsafe to be called externally")
+		Err(Error::UnsafeRpcCalled(e)) => {
+			assert_eq!(e.to_string(), "RPC call is unsafe to be called externally")
 		}
 	);
 }