Add integration with AI Horde

And now to go full circle: Please add an integration with the AI Horde, for your users without access to a powerful enough GPU.

The AI Horde provides a free asynchronous REST API you can integrate with where you can send the payload and receive one or more SD images back. You can also use it to integrate with LLMs or even just simple post-processors like upscalers and face-fixers.

Full API documentation: https://aihorde.net/api