Support Stable Diffusion

[ullenboom]

According to https://docs.spring.io/spring-ai/reference/api/imageclient.html Spring AI only supports two commercial image generators. It would be nice to include Stable Diffusion in the lineup as an alternative, particularly for demonstration purposes. However, I recognize that calling Python programs, as required for Stable Diffusion, involves a more complex process compared to the straightforward REST calls currently in use.