approval-voting metrics (#2483)

* approval-voting metrics

* metric: approvals produced

polkadot/node/service/src/grandpa_support.rs

@@ -57,7 +57,7 @@ impl ApprovalCheckingDiagnostic {
 				Some(prometheus_endpoint::register(
 					prometheus_endpoint::Histogram::with_opts(
 						prometheus_endpoint::HistogramOpts::new(
-							"approval_checking_finality_lag",
+							"parachain_approval_checking_finality_lag",
 							"How far behind the head of the chain the Approval Checking protocol wants to vote",
 						).buckets(vec![1.0, 2.0, 3.0, 4.0, 5.0, 10.0, 20.0, 30.0, 40.0, 50.0])
 					)?,

polkadot/node/service/src/lib.rs

@@ -497,6 +497,7 @@ where
 		approval_voting: ApprovalVotingSubsystem::with_config(
 			approval_voting_config,
 			keystore.clone(),
+			Metrics::register(registry)?,
 		)?,
 		gossip_support: GossipSupportSubsystem::new(),
 	};