feat: allow watch onset sleep detection

[austinkimchi]

Is your feature request related to a problem? Please describe.
I want my smart alarm to be automatically set when I have an Apple Watch device on.

Describe the solution you'd like
Detect the onset of sleep and set my smart alarm bedtime accordingly.

[austinkimchi]

There's an issue right now with a message appearing on the Apple Watch.
"SleepFocus was running in the background but failed to play an alarm..."
I don't know if this is a general safeguard or if it's a bug by our end or by Apple.
Refer to https://www.reddit.com/r/sleepcycle/comments/1d6xib8/anyone_else_notice_issues_with_alarm_when_set_on/

Screenshots
Needs screenshots here next time it happens.