Return numberMatched if in STA response (#1259)

Attempt to return `@iot.count` in included in response. Including the query param `'$count' = 'true'` is costly on the SensorThings API endpoint when accessing the Observations entity. Some STA endpoints are including the count as a default.

pygeoapi/provider/sensorthings.py

@@ -249,9 +249,13 @@ class SensorThingsProvider(BaseProvider):
 
         # Make features
         response = self._get_response(url=self._url, params=params)
-        v = response.get('value')
+
+        matched = response.get('@iot.count')
+        if matched:
+            fc['numberMatched'] = matched
 
         # Query if values are less than expected
+        v = response.get('value')
         while len(v) < limit:
             try:
                 LOGGER.debug('Fetching next set of values')