Issue #3144069: Support date range field

config/schema/datetime_flatpickr.schema.yml

-field.widget.settings.datetime_flatpickr:
+datetime_flatpickr_config:
   type: mapping
-  label: 'Datetime flat pickr display format settings'
   mapping:
     dateFormat:
       type: string
@@ -65,3 +64,11 @@ field.widget.settings.datetime_flatpickr:
     weekNumbers:
       type: boolean
       label: 'Week numbers'
+
+field.widget.settings.datetime_flatpickr:
+  label: 'Datetime flatpickr display format settings'
+  type: datetime_flatpickr_config
+
+field.widget.settings.datetime_range_flatpickr:
+  label: 'Datetime range flatpickr display format settings'
+  type: datetime_flatpickr_config