Add field type for fields that accept opening_hours syntax

[1ec5]

The schema should have a dedicated field type for fields that accept the opening_hours syntax, to wit:

• Hours (opening_hours)
• COVID-19 Pandemic Hours (opening_hours:covid19)
• Service Times (service_times)
• Collection Times (collection_times)

This would make it possible to implement a specialized field for all these keys at once as part of openstreetmap/iD#974 instead of having to hard-code them in the iD codebase.