Add Multi-Modality Support for OpenAI

- Implemented a MediaContent abstraction within the OpenAiApi to handle text and image inputs.
 - Response message content remains a plain String, ensuring backward compatibility.
 - Extended the OpenAiChatClient request creation process to seamlessly map Spring AI Messages with
   Media content to the low-level OpenAiApi MediaContent types.
 - Added integration tests for embedded and URL images, covering both synchronous and streaming calls.
 - Updated the OpenAI class diagram to reflect the new media content types provided by the OpenAI API.
 - Incorporated a chapter on multi-modality within the openai-chat.adoc documentation.
 - Improve the openai multimoality doc

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

@@ -141,6 +141,57 @@ You can register custom Java functions with the OpenAiChatClient and have the Op
 This is a powerful technique to connect the LLM capabilities with external tools and APIs.
 Read more about xref:api/chat/functions/openai-chat-functions.adoc[OpenAI Function Calling].
 
+== Multimodal
+
+Multimodality refers to a model's ability to simultaneously understand and process information from various sources, including text, images, audio, and other data formats.
+Presently, the OpenAI `gpt-4-visual-preview` model offers multimodal support. Refer to the link:https://platform.openai.com/docs/guides/vision[Vision] guide for more information.
+
+The OpenAI link:https://platform.openai.com/docs/api-reference/chat/create#chat-create-messages[User Message API] can incorporate a list of base64-encoded images or image urls with the message.
+Spring AI’s link:https://github.com/spring-projects/spring-ai/blob/main/spring-ai-core/src/main/java/org/springframework/ai/chat/messages/Message.java[Message] interface facilitates multimodal AI models by introducing the link:https://github.com/spring-projects/spring-ai/blob/main/spring-ai-core/src/main/java/org/springframework/ai/chat/messages/Media.java[Media] type.
+This type encompasses data and details regarding media attachments in messages, utilizing Spring’s `org.springframework.util.MimeType` and a `java.lang.Object` for the raw media data.
+
+Below is a code example excerpted from link:https://github.com/spring-projects/spring-ai/blob/main/models/spring-ai-openai/src/test/java/org/springframework/ai/openai/OpenAiChatClientIT.java[OpenAiChatClientIT.java], illustrating the fusion of user text with an image.
+
+[source,java]
+----
+byte[] imageData = new ClassPathResource("/multimodal.test.png").getContentAsByteArray();
+
+var userMessage = new UserMessage("Explain what do you see on this picture?",
+        List.of(new Media(MimeTypeUtils.IMAGE_PNG, imageData)));
+
+ChatResponse response = chatClient.call(new Prompt(List.of(userMessage),
+        OpenAiChatOptions.builder().withModel(OpenAiApi.ChatModel.GPT_4_VISION_PREVIEW.getValue()).build()));
+----
+
+or the image URL equivalent:
+
+[source,java]
+----
+var userMessage = new UserMessage("Explain what do you see on this picture?",
+        List.of(new Media(MimeTypeUtils.IMAGE_PNG,
+                "https://docs.spring.io/spring-ai/reference/1.0-SNAPSHOT/_images/multimodal.test.png")));
+
+ChatResponse response = chatClient.call(new Prompt(List.of(userMessage),
+        OpenAiChatOptions.builder().withModel(OpenAiApi.ChatModel.GPT_4_VISION_PREVIEW.getValue()).build()));
+----
+
+TIP: you can pass multiple images as well.
+
+It takes as an input the `multimodal.test.png` image:
+
+image::multimodal.test.png[Multimodal Test Image, 200, 200, align="left"]
+
+along with the text message "Explain what do you see on this picture?", and generates a response like this:
+
+----
+This is an image of a fruit bowl with a simple design. The bowl is made of metal with curved wire edges that
+create an open structure, allowing the fruit to be visible from all angles. Inside the bowl, there are two
+yellow bananas resting on top of what appears to be a red apple. The bananas are slightly overripe, as
+indicated by the brown spots on their peels. The bowl has a metal ring at the top, likely to serve as a handle
+for carrying. The bowl is placed on a flat surface with a neutral-colored background that provides a clear
+view of the fruit inside.
+----
+
 == Sample Controller
 
 https://start.spring.io/[Create] a new Spring Boot project and add the `spring-ai-openai-spring-boot-starter` to your pom (or gradle) dependencies.
@@ -239,7 +290,7 @@ The https://github.com/spring-projects/spring-ai/blob/main/models/spring-ai-open
 
 Following class diagram illustrates the `OpenAiApi` chat interfaces and building blocks:
 
-image::openai-chat-api.png[OpenAiApi Chat API Diagram]
+image::openai-chat-api.jpg[OpenAiApi Chat API Diagram, width=1000, align="center"]
 
 Here is a simple snippet how to use the api programmatically: