rpc server: add rate limiting middleware (#3301)

Add RPC server rate limiting which can be utilized by the CLI
`--rpc-rate-limit <calls/per minute>`

Resolves first part of
https://github.com/paritytech/polkadot-sdk/issues/3028

//cc @PierreBesson @kogeler  you might be interested in this one

---------

Co-authored-by: James Wilson <james@jsdw.me>
Co-authored-by: Xiliang Chen <xlchen1291@gmail.com>

substrate/client/cli/src/commands/run_cmd.rs

@@ -34,7 +34,10 @@ use sc_service::{
 	ChainSpec, Role,
 };
 use sc_telemetry::TelemetryEndpoints;
-use std::net::{IpAddr, Ipv4Addr, SocketAddr};
+use std::{
+	net::{IpAddr, Ipv4Addr, SocketAddr},
+	num::NonZeroU32,
+};
 
 /// The `run` command used to run a node.
 #[derive(Debug, Clone, Parser)]
@@ -82,6 +85,15 @@ pub struct RunCmd {
 	)]
 	pub rpc_methods: RpcMethods,
 
+	/// RPC rate limiting (calls/minute) for each connection.
+	///
+	/// This is disabled by default.
+	///
+	/// For example `--rpc-rate-limit 10` will maximum allow
+	/// 10 calls per minute per connection.
+	#[arg(long)]
+	pub rpc_rate_limit: Option<NonZeroU32>,
+
 	/// Set the maximum RPC request payload size for both HTTP and WS in megabytes.
 	#[arg(long, default_value_t = RPC_DEFAULT_MAX_REQUEST_SIZE_MB)]
 	pub rpc_max_request_size: u32,
@@ -399,6 +411,10 @@ impl CliConfiguration for RunCmd {
 		Ok(self.rpc_max_subscriptions_per_connection)
 	}
 
+	fn rpc_rate_limit(&self) -> Result<Option<NonZeroU32>> {
+		Ok(self.rpc_rate_limit)
+	}
+
 	fn transaction_pool(&self, is_dev: bool) -> Result<TransactionPoolOptions> {
 		Ok(self.pool_config.transaction_pool(is_dev))
 	}