[Task] Support in DB for chat history saving/restoration

[alapha23]

Description

The messages will be updated in the DB once a new message is added to the conversation.

Once the user closes and comes back to the conversation, the conversation will be fetched and restored from the DB

Tasks

• [x] Backend API Save Chat History in DB
• [x] Backend API Restore Chat History

[alapha23]

PR https://github.com/alapha23/UrbanScholar/pull/16