refactor(timezone): add timezone to schedules

[mforesti]

Summary

In this PR, the timezone is added to the schedules.

Impact

• App
• Supabase functions
• Supabase migration
• CI / GitHub
• pubspec.yaml

Testing steps

• Add a new schedule with a different timezone than the one of the device.
• Check wether the time shown in the schedule instances aligns with you timezone.
• Add replies and default rules. The buttons must behave correctly

Open points

• Add search capability to the timezone list in the schedule form.
• Show to the user the timezone of the event and the time at the remote location when the timezone differs from the local one.
• Add test case to cover timezone

[mforesti]

Suggested change

	} else if (snapshot.hasError) {
	return Text('Error: ${snapshot.error}');
	} else if (!snapshot.hasData ||
	snapshot.data!.isEmpty) {
	return Text('No data');
	} else {
	} else if (snapshot.hasError ||
	!snapshot.hasData ||
	snapshot.data!.isEmpty) {
	return Text('--:--');
	} else {

[mforesti]

This could be a bit more user-friendly.