core: ardupilot-manager: support non-USB serial autopilot connections

### Current behaviour

Flight controllers can currently only have a serial connection to the Raspberry Pi via a USB port. This unnecessarily prevents connecting an autopilot via a UART using the GPIO pins, which can be useful for space-saving, as well as general accessibility (more available interfaces -> higher chance of at least one of them being appropriate for a given application).

Issue first realised in [this forum post](https://discuss.bluerobotics.com/t/connect-rpi-to-ardu-using-gpio-uart/14055).

### Expected or desired behaviour

- **Ideally:** all serial ports should be considered as potential autopilot candidates - not just the ones identified as USB
- Initial attempt in #1580, although as per [discussion there](https://github.com/bluerobotics/BlueOS-docker/pull/1580#issuecomment-1499031926), that approach may only partially resolve the issue
- **Minimally:** support manual overrides, for users who know the path/name for the serial port their device is connected to

### Prerequisites

- [X] I have checked to make sure that a similar request has not already been filed or fixed.