Include opponent's name in turn notification

[LForchini]

Fixes #

Proposed Changes

• Change the format of the notification when it's your move in correspondence games to remove the game id and instead include the username of the opponent.

Motivation

I feel that the game id does not have any use in the notification, whereas I think the opponents name would be more useful.

I am new to this codebase so any advice would be useful, specifically if there's an established method for finding the name of the opponent.

[github-actions]

Uffizzi Preview deployment-52540 was deleted.

[anoek]

Thanks!