fix(frontend): wrong placeholder message date (#2023)

# Description

Please include a summary of the changes and the related issue. Please
also include relevant motivation and context.

## Checklist before requesting a review

Please delete options that are not relevant.

- [ ] My code follows the style guidelines of this project
- [ ] I have performed a self-review of my code
- [ ] I have commented hard-to-understand areas
- [ ] I have ideally added tests that prove my fix is effective or that
my feature works
- [ ] New and existing unit tests pass locally with my changes
- [ ] Any dependent changes have been merged

## Screenshots (if appropriate):

frontend/app/chat/[chatId]/utils/generatePlaceHolderMessage.ts

@@ -9,14 +9,10 @@ export const generatePlaceHolderMessage = ({
   user_message,
   chat_id,
 }: GeneratePlaceHolderMessageProps): ChatMessage => {
-  const message_id = new Date().getTime().toString();
-  const message_time = new Date().toISOString();
-  const assistant = "";
-
   return {
-    message_id,
+    message_id: new Date().getTime().toString(),
-    message_time,
+    message_time: new Date(new Date().setDate(new Date().getDate() + 1)).toISOString(),
-    assistant,
+    assistant: 'Thinking..',
     chat_id,
     user_message,
   };