Subscribe (single-use) to a players match

When a friend (or multiple friends) are in a match, people might be waiting for their game(s) to finish.

To allow them to play together, we can let users subscribe to the match-finish event. Since it will be checked anyways, this doesn't cost us anything (only sending a discord embed).

An idea is: /subscribe match-end [user] for a simple match complete notification. This will expire once the message is sent once. /subscribe match-end [user-list] for when someone wants to track multiple summoners and see when ALL are out of game. Only a single message should be sent. I'd like to point out this should be a personal Discord message.

General subscription expiry rules:

subscription time is over 2 hours old
subscribee's gameId changes

Another reason the subscription may expire is when the subscriber enters a match. However, we probably don't have the Discord->summoner name connection. Which of course is another question: should we let people /link [summoner] and what can we do with this? (open new issue if interesting)

There may be more ideas here, but this simple feature may be nice.

freshcoders / discorki

Subscribe (single-use) to a players match #73