Spring-ai [OpenAI] Image Client always overwrite model from application properties with default value

Bug description The spring.ai.openai.image.options.model value is always overwritten by the model default value defined in the OpenAiImageOptions class.

Environment Spring AI: 1.0.0-SNAPSHOT Java 21

Expected behavior The spring.ai.openai.image.options.model value is only overwritten if a model is explicitly defined per-request in the ImagePrompt.

Minimal Complete Reproducible example App reproducing the error: https://github.com/ThomasVitale/llm-apps-java-spring-ai/tree/main/08-image-models/image-models-openai. The spring.ai.openai.image.options.model property is set to dall-e-2, but it's always overwritten with dall-e-3.