[#1244] nats: Split client creation into 2 stages

Create and connect to an endpoint using separate functions.

Signed-off-by: Evgenii Stratonikov <evgeniy@nspcc.ru>

cmd/neofs-node/main.go

@@ -89,6 +89,7 @@ func initApp(c *cfg) {
 }
 
 func bootUp(c *cfg) {
+	connectNats(c)
 	serveGRPC(c)
 	makeAndWaitNotaryDeposit(c)
 	bootstrapNode(c)