Add a TTL to the events

[ahmadbky]

We need to add a TTL (time-to-live) to the events of the new event system. This TTL can be null (or infinite) so the players can play an event forever ; but it remains useful especially for the Lol-Cup, because it marks an end to the event.

The behavior of this should be to provide a new boolean field for the event edition's information, like expired, that tells if this edition is still playable or not. If the edition has expired, it is not shown on the website's dropdown. However, the pages at /event/XX/YY should remain visitable. If the event has expired, the next update field should be null. When the time comes where events would be integrated in the TP, the event would still be displayed but as expired and thus not playable. Any post to routes related to this event would result to an error. However, everything related to this edition should remain stored. This means that the related MX mappack in Redis should remain persistent, and the next edition ID would follow it.