Allow to specify multiple relay chain RPC urls for collator node (#1880)

* Allow specification of multiple urls for relay chain rpc nodes

* Add pooled RPC client basics

* Add list of clients to pooled client

* Improve

* Forward requests to dispatcher

* Switch clients on error

* Implement rotation logic

* Improve subscription handling

* Error handling cleanup

* Remove retry from rpc-client

* Improve naming

* Improve documentation

* Improve `ClientManager` abstraction

* Adjust zombienet test

* Add more comments

* fmt

* Apply reviewers comments

* Extract reconnection to extra method

* Add comment to reconnection method

* Clean up some dependencies

* Fix build

* fmt

* Provide alias for cli argument

* Apply review comments

* Rename P* to Relay*

* Improve zombienet test

* fmt

* Fix zombienet sleep

* Simplify zombienet test

* Reduce log clutter and fix starting position

* Do not distribute duplicated imported and finalized blocks

* fmt

* Apply code review suggestions

* Move building of relay chain interface to `cumulus-client-service`

* Refactoring to not push back into channel

* FMT

client/relay-chain-interface/src/lib.rs

@@ -51,11 +51,11 @@ pub enum RelayChainError {
 	BlockchainError(#[from] sp_blockchain::Error),
 	#[error("State machine error occured: {0}")]
 	StateMachineError(Box<dyn sp_state_machine::Error>),
-	#[error("Unable to call RPC method '{0}' due to error: {1}")]
-	RpcCallError(String, JsonRpcError),
+	#[error("Unable to call RPC method '{0}'")]
+	RpcCallError(String),
 	#[error("RPC Error: '{0}'")]
 	JsonRpcError(#[from] JsonRpcError),
-	#[error("Unable to reach RpcStreamWorker: {0}")]
+	#[error("Unable to communicate with RPC worker: {0}")]
 	WorkerCommunicationError(String),
 	#[error("Scale codec deserialization error: {0}")]
 	DeserializationError(CodecError),