feat: Allow users set live cron schedules

[Zibbp]

Users now have the ability to set the schedule live channels are checked. This can be accomplished by adding an environment variable to the Ceres docker service.

LIVE_CRON_SCHEDULE=EVERY_10_MINUTES

For a list of valid cron expressions, visit the NestJS schedule package. This variable will only accept the text cron expression and not the actual cron expression, example: EVERY_MINUTE is valid */1 * * * * is not valid.

If the variable is not set it will default to 5 minutes. If the user enters an incorrect cron expression it will default to 5 minutes and notify them in the logs that it is incorrect.

Note: Values below five minutes may result in the thumbnail missing for live streams. This is because Twitch does not update thumbnails when the stream starts but instead on a schedule.