Add a board level config `upload.gpiostring`#664

Miceuz wants to merge 1 commit intoplatformio:developplatformio/platform-ststm32:developfrom

Miceuz:feature/add_gpio_controll_for_serial_uploadMiceuz/platform-ststm32:feature/add_gpio_controll_for_serial_uploadCopy head branch name to clipboard