Make network_config_path an Option (#5661)

* Make network_config_path an Option

* Fix network tests

* Use None as the network config path

* Fix cli

* Don't make PathBuf an Option in a cli context

substrate/utils/browser/src/lib.rs

@@ -49,7 +49,7 @@ where
 		format!("{} (Browser)", name),
 		"unknown",
 		Default::default(),
-		&std::path::PathBuf::new(),
+		None,
 	);
 	network.boot_nodes = chain_spec.boot_nodes().to_vec();
 	network.transport = TransportConfig::Normal {