[MAIN-370] POC Address server side timer features for turn-based-games

[kevo1ution]

Address server side timer feature for turn-based games boardgameio/boardgame.io/issues/92

1. Set a timer so that a user-defined function can modify the state of the room when that timeout is reached onTimeout
2. Ability to stop a timer after setting it. (e.g. when a player makes a move)
3. Timers can be set at any time in the future (anything less than 10 seconds will not have as good execution guarantees).

Experimental usage instructions

# in the root of your game folder
npm i -S @urturn/[email protected]

Docs on how to use it! https://board-games-dev-e8c04--pr207-main-370-timers-poc-qvwllgsf.web.app/docs/Advanced/timer-triggers

We are still iterating on the exact interface of this so please provide feedback in our discord or on the pr!

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[github-actions]

Visit the preview URL for this PR (updated for commit eb1350d):

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