openapi/schemas/extent: Clarifications

- features -> data (generic for common)
- correcting open -> half-bounded as per opengeospatial/ogcapi-common#196

openapi/schemas/common-geodata/extent.yaml

@@ -11,7 +11,7 @@ description: |-
 type: object
 properties:
   spatial:
-    description: The spatial extent of the features in the collection.
+    description: The spatial extent of the data in the collection.
     type: object
     properties:
       bbox:
@@ -109,7 +109,7 @@ properties:
             temporal coordinate reference system specified in `trs`. By default
             this is the Gregorian calendar.
 
-            The value `null` is supported and indicates an open time interval.
+            The value `null` for start or end time is supported and indicates a half-bounded time interval.
           type: array
           minItems: 2
           maxItems: 2