Use sign_with for signing grandpa's outgoing message (#6178)

* Use sign_with and stop using `Pair`

* PR feedback

* Remove clone

* Transfer ownership of public to sign_message

* Use Option

* Simplify code

* Fix error message

* Pass keystore as ref

* Pass keystore properly

* Fix tests

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

@@ -148,7 +148,7 @@ pub fn new_full(config: Configuration) -> Result<impl AbstractService, ServiceEr
 	// if the node isn't actively participating in consensus then it doesn't
 	// need a keystore, regardless of which protocol we use below.
 	let keystore = if role.is_authority() {
-		Some(service.keystore())
+		Some(service.keystore() as sp_core::traits::BareCryptoStorePtr)
 	} else {
 		None
 	};