Comment game

[elodieburtin]

Allow to add a free text comment when creating/updating a game (useful e.g. for Unlock to specify which game was performed)

[waliens]

Should we extend this to other entities ? (board games, timers...)

[FServais]

I would say game is more important, maybe timer. We can do that first, try to make it generic, then see for other entities later :)

[waliens]

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