Attempt to use Check-Ins for server instance monitoring

[devSparkle]

Sentry recently introduced a Check-Ins API intended to be used for CRON jobs. We could attempt to use this to display useful information about the amount of servers running, and potentially detect crashes.

A server would have to send a signal when closing to let Sentry know that the "CRON task" is no longer necessary. Should it fail to do this, Sentry (and the user) will assume a crash. This would effectively monitor data that Roblox developers have, at this time, no other way of monitoring.