[Scheduler][FrameworkBundle] Add SchedulerBundle

The scheduler services move to the Scheduler component, which now provides its own
bundle and the "scheduler" configuration. The "framework.scheduler" configuration
becomes an alias of it.

Since the scheduler only provides Messenger transports, its services are dropped when
no Messenger transport factory is registered; enabling Messenger is required only when
a schedule or a task is declared, which AddScheduleMessengerPass now reports.