Add more metrics to prometheus (#5034)

* Add a few things

* Add finality_grandpa_round

* fix fg tests

* Nitpicks

* Nitpicks

* Fix name of prometheus crate

substrate/client/network/src/error.rs

@@ -45,6 +45,8 @@ pub enum Error {
 		/// The second peer id that was found for the bootnode.
 		second_id: PeerId,
 	},
+	/// Prometheus metrics error.
+	Prometheus(prometheus_endpoint::PrometheusError)
 }
 
 // Make `Debug` use the `Display` implementation.
@@ -60,6 +62,7 @@ impl std::error::Error for Error {
 			Error::Io(ref err) => Some(err),
 			Error::Client(ref err) => Some(err),
 			Error::DuplicateBootnode { .. } => None,
+			Error::Prometheus(ref err) => Some(err),
 		}
 	}
 }