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

cumulus/client/relay-chain-minimal-node/src/lib.rs

@@ -85,7 +85,7 @@ fn build_authority_discovery_service<Block: BlockT>(
 pub async fn build_minimal_relay_chain_node(
 	polkadot_config: Configuration,
 	task_manager: &mut TaskManager,
-	relay_chain_url: Url,
+	relay_chain_url: Vec<Url>,
 ) -> RelayChainResult<(Arc<(dyn RelayChainInterface + 'static)>, Option<CollatorPair>)> {
 	let client = cumulus_relay_chain_rpc_interface::create_client_and_start_worker(
 		relay_chain_url,