Add player profile public toggle

## Player profile public flag

Players who opt in can show their identity in locations like https://api.openfront.io/leaderboard/public/ffa and on the game summary screens.

## Setting the public flag

To set the profile to public send `POST /users/@me` to `https://api.openfront.io` with the body: `{"public": true}`.

## Implementation

Add a toggle button to enable or disable the public flag.

May depend on #1728