node: spawn block authoring and grandpa voter as blocking tasks (#6446)

* service: add spawner for essential tasks

* node: spawn block authoring and grandpa voter as blocking tasks

* Apply suggestions from code review

Co-authored-by: Bastian Köcher <bkchr@users.noreply.github.com>

substrate/bin/node-template/node/src/service.rs

@@ -142,7 +142,7 @@ pub fn new_full(config: Configuration) -> Result<impl AbstractService, ServiceEr
 
 		// the AURA authoring task is considered essential, i.e. if it
 		// fails we take down the service with it.
-		service.spawn_essential_task("aura", aura);
+		service.spawn_essential_task_handle().spawn_blocking("aura", aura);
 	}
 
 	// if the node isn't actively participating in consensus then it doesn't
@@ -184,7 +184,7 @@ pub fn new_full(config: Configuration) -> Result<impl AbstractService, ServiceEr
 
 		// the GRANDPA voter task is considered infallible, i.e.
 		// if it fails we take down the service with it.
-		service.spawn_essential_task(
+		service.spawn_essential_task_handle().spawn_blocking(
 			"grandpa-voter",
 			sc_finality_grandpa::run_grandpa_voter(grandpa_config)?
 		);