Adding the messagesHistory method in the OpenAiController.

Author: n-o-u-r-h-a-n

sample-code/spring-app/src/main/java/com/sap/ai/sdk/app/controllers/OpenAiController.java

@@ -41,6 +41,19 @@ Object chatCompletion(
     return response.getContent();
   }
 
+  @GetMapping("/messagesHistory")
+  @Nonnull
+  Object messagesHistory(
+      @Nullable @RequestParam(value = "format", required = false) final String format,
+      @Nonnull @RequestParam(value = "previousMessage", defaultValue = "Who is the prettiest")
+          final String previousMessage) {
+    final var response = service.messagesHistory(previousMessage);
+    if ("json".equals(format)) {
+      return response;
+    }
+    return response.getContent();
+  }
+
   @SuppressWarnings("unused") // The end-to-end test doesn't use this method
   @GetMapping("/streamChatCompletionDeltas")
   @Nonnull