Bug: Boards - CSV export of a Person property exports user IDs instead of usernames

Steps to reproduce the behavior

Reviving https://github.com/mattermost/focalboard/issues/2990

1. Go to a board
2. Add a person property to a card and assign a user
3. Click on ... > Export to CSV
4. Open the exported file and observe the person property - it shows the user id instead of the username

Expected behavior

We use boards extensively, but it is currently difficult to match a person with User IDs. Username is expected instead for better understanding.

Screenshots (optional)

Edition and Platform

• Edition: Mattermost Boards (plugin)
• Version: v7.11.4
• Browsers and Desktop apps