feat: scheduler fn support

[Salakar]

Testing

Deployed the following sample:

from firebase_functions import scheduler_fn


@scheduler_fn.on_schedule(
    schedule="* * * * *",
    timezone=scheduler_fn.Timezone("America/Los_Angeles"),
)
def example(event: scheduler_fn.ScheduledEvent) -> None:
    print("Hello from scheduled function!")
    print(event.job_name)
    print(event.schedule_time)

Deployment is successful:

Schedule runs and prints:

[taeold]

minor nits

[taeold]

nit* This is great! I'd been fine with string, but parsing it sounds extra helpful!