[Spacebot] Message user when card is being activated

[chungl]

A recurring contact request arises from people reactivating their membership and not immediately being able to get into the door. Since there's a bit of latency involved in activating a card, it would be nice if spacebot could message the member via slack to confirm that their membership is active and their card will be reactivated within a few minutes. We could set expectations that they will receive a followup message when the card becomes active, and that if the card is not active within 5 minutes they should reach out to us for help