Added download chat history button for AI Assistant

[JoelWiebe]

For the AI Assistant, log all chat messages to the data base and create a download button where each teacher can download their own chat history.

Details

• Create a database schema for saving chat logs, including the teacher's user ID, role (whether user or assistant), the timestamp, the board ID, and the content
• Each time a user creates a prompt, save the prompt with the 'user' role
• Each time the AI assistant creates a response, save the response with the 'assistant' role
• Create a Download Chat History button in the AI assistant tab
• When the download button is pressed, retrieve the entire chat history and save as a CSV file that is downloaded by the client

Test:

• Ensure all previous AI Assistant commands work (creating a bucket, move a post, access vote, tag, title, and content data from posts)
• Log history can be downloaded when history is empty and has content
• Different teachers should download only their own chat history

Closes #625