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-gossip/src/state_machine.rs

@@ -197,11 +197,6 @@ impl<B: BlockT> ConsensusGossip<B> {
 
 	/// Handle new connected peer.
 	pub fn new_peer(&mut self, network: &mut dyn Network<B>, who: PeerId, role: ObservedRole) {
-		// light nodes are not valid targets for consensus gossip messages
-		if role.is_light() {
-			return;
-		}
-
 		tracing::trace!(
 			target:"gossip",
 			%who,