Read and control Gecko spa controller (in.YE, in.XM, etc.)

**Describe the problem you have/What new integration you would like**

The [Gecko IN.YE](https://www.geckodocs.com/yseries) Spa main controller has the option to be controlled via an external [IN.Touch2](https://geckoalliance.com/products/in-touch-2/) WiFi connected device (official link broken, a random example [here](https://www.amazon.com/GECKO-Touch-Internet-Module-Version/dp/B08L3TMHS9) ).
There is an extensive [discussion ongoing in the Home Assistant feature-request forum](https://community.home-assistant.io/t/gecko-in-touch2-integration-spa-wireless-remote-control-module/150764) but it's a mix of hijacking and reverse-engineering the C0 interface and integrating the OEM IN.Link2 device. So let's try to split the hijacking part to another discussion.

**Please describe your use case for this integration and alternatives you've tried:**

Find a way to interact with the IN.YE spa controllers without having to buy an IN.Touch2.
RS485 on the C0 port seem like the best bet at the moment but looking around on the main-board there are also I2C mentioned on some connectors.

Even if the discussion is posted in the ESPHome forum I don't see the need to restrict it for ESPHome only. Arduino sketches or even PC communication could be helpful to share, and eventually it should be portable to ESPHome which in my opinion has the widest usability and good interaction with Home Assistant.

**Additional context**

Useful links from the other forum.

I took some photos of the additional soldering points in the main-board, unfortunate for me the RS485 (and remote relays for whatever might be used for) pins seem a no-go since no components mounted. But the I2C could maybe work. Still the C0 - C2 ports are maybe the better bet since they are for communication the external devices.