Allow pins 0 and 1 as RTS/DTR for USB UART Bridge (#1864)

* Allow pins 0 and 1 as RTS/DTR for USB UART Bridge
* add logic to gpio_scene_usb_uart_config, fix flow_pins
* fixing count of pins
* disable PC0,PC1 RTS/DTR when using LPUART
* add logic to ensure flow pins dont overlap with uart lines

Co-authored-by: あく <alleteam@gmail.com>

applications/main/gpio/gpio_app_i.h

@@ -24,6 +24,7 @@ struct GpioApp {
     Widget* widget;
 
     VariableItemList* var_item_list;
+    VariableItem* var_item_flow;
     GpioTest* gpio_test;
     GpioUsbUart* gpio_usb_uart;
     UsbUartBridge* usb_uart_bridge;