grandpa: enable light clients to participate in gossip (#8796)

* network: allow gossiping to light clients

* grandpa: gossip global messages to light clients

* grandpa: don't send neighbor packets to light clients

* grandpa: fix tests

* grandpa: export run_grandpa_observer

* node: run grandpa observer on light client

* node: start network at end

* Use wasm_timer in finality-grandpa

Co-authored-by: Pierre Krieger <pierre.krieger1708@gmail.com>

substrate/client/network/src/config.rs

@@ -141,6 +141,11 @@ impl Role {
 	pub fn is_authority(&self) -> bool {
 		matches!(self, Role::Authority { .. })
 	}
+
+	/// True for `Role::Light`
+	pub fn is_light(&self) -> bool {
+		matches!(self, Role::Light { .. })
+	}
 }
 
 impl fmt::Display for Role {