ERT: Add RSSI to app UI.

firmware/application/ert_app.cpp

@@ -130,6 +130,7 @@ ERTAppView::ERTAppView(NavigationView&) {
 		&field_rf_amp,
 		&field_lna,
 		&field_vga,
+		&rssi,
 		&recent_entries_view,
 	} });
 

firmware/application/ert_app.hpp

@@ -145,6 +145,10 @@ private:
 		{ 18 * 8, 0 * 16 }
 	};
 
+	RSSI rssi {
+		{ 21 * 8, 0, 6 * 8, 4 },
+	};
+
 	MessageHandlerRegistration message_handler_packet {
 		Message::ID::ERTPacket,
 		[this](Message* const p) {