Enable async backing by default for Rococo/Westend

This change is mainly for people running the local variants. They can
directly start with async backing.

polkadot/node/service/src/chain_spec.rs

@@ -120,7 +120,7 @@ pub fn wococo_config() -> Result<RococoChainSpec, String> {
 fn default_parachains_host_configuration(
 ) -> polkadot_runtime_parachains::configuration::HostConfiguration<polkadot_primitives::BlockNumber>
 {
-	use polkadot_primitives::{MAX_CODE_SIZE, MAX_POV_SIZE};
+	use polkadot_primitives::{AsyncBackingParams, MAX_CODE_SIZE, MAX_POV_SIZE};
 
 	polkadot_runtime_parachains::configuration::HostConfiguration {
 		validation_upgrade_cooldown: 2u32,
@@ -151,6 +151,11 @@ fn default_parachains_host_configuration(
 		relay_vrf_modulo_samples: 2,
 		zeroth_delay_tranche_width: 0,
 		minimum_validation_upgrade_delay: 5,
+		scheduling_lookahead: 2,
+		async_backing_params: AsyncBackingParams {
+			max_candidate_depth: 3,
+			allowed_ancestry_len: 2,
+		},
 		..Default::default()
 	}
 }