[Akeru Web App] Implement Message Sending Functionality

[multipletwigs]

Description:
Enable users to send messages using the input area. When the send button is clicked, the message should appear in the thread window. Please refer to our backend endpoint on submitting a message to a thread.

Tasks:

1. Capture input from the text box.
2. Add the message to the thread window upon clicking the send button.
3. Clear the input box after the message is sent.
4. You may consider using optimistic updates for better ui feedback when sending messages.
5. You may also call the thread/run endpoint after this step to receive a response after sending a message.