Add JSON Schema for Provider `service_area` API

[hunterowens]

Since #110, we should add JSON schema definitions into this before 0.3.0

[hunterowens]

Ref #110, and @asadowns / @babldev, we might not want service areas as we can determine it from service_area_start status_change events.

[hunterowens]

This is removed in #203, so closing.