fix: Fixed the example code error in multimodality (#4475)

Auto-cherry-pick to 1.0.x Fixes #4475 Signed-off-by: Sun Yuhan <sunyuhan1998@users.noreply.github.com> Co-authored-by: Sun Yuhan <sunyuhan1998@users.noreply.github.com>

Author: sunyuhan1998

spring-ai-docs/src/main/antora/modules/ROOT/pages/api/multimodality.adoc

@@ -41,9 +41,10 @@ For most of the multimodal LLMs, the Spring AI code would look something like th
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 var imageResource = new ClassPathResource("/multimodal.test.png");
 
-var userMessage = new UserMessage(
-"Explain what do you see in this picture?", // content
-new Media(MimeTypeUtils.IMAGE_PNG, this.imageResource)); // media
+var userMessage = UserMessage.builder()
+ .text("Explain what do you see in this picture?") // content
+ .media(new Media(MimeTypeUtils.IMAGE_PNG, this.imageResource)) // media
+ .build();
 
 ChatResponse response = chatModel.call(new Prompt(this.userMessage));
 ----