NetworkSettings: Use helper script to write config

This change allows us to not run the app with elevated privileges.

It uses the Escalator to call a helper and passes the settings as
JsonObject to it.

Userland/Applications/NetworkSettings/NetworkSettingsWidget.h

@@ -32,6 +32,8 @@ private:
 
     void on_switch_adapter(DeprecatedString const& adapter);
     void on_switch_enabled_or_dhcp();
+    ErrorOr<void> apply_settings_impl();
+    ErrorOr<Optional<JsonObject>> create_settings_object();
 
     HashMap<DeprecatedString, NetworkAdapterData> m_network_adapters;
     Vector<DeprecatedString> m_adapter_names;