Add (start|end)_date_type properties to control-statement
Add (start|end)_date_type properties to control-statement

I think probably all schemas which have start/end date properties should have these too, so the bot can be explicit about it. But we would need to think about it more before applying to all schemas. We definitely need these for some upcoming control-statement bot changes though, so for now just add them here.

There is also a question of whether they should be _required_ when the equivalent date property is present. However currently no schemas do this so I'm sticking with consistency for now.

openc/openc-schema