Make successUri mandatory in subscriber

It's mandatory in the standard.

Thx @ricardogsilva !

pygeoapi/api.py

@@ -3491,12 +3491,22 @@ def execute_process(self, request: Union[APIRequest, Any],
         data_dict = data.get('inputs', {})
         LOGGER.debug(data_dict)
 
-        subscriber_dict = data.get('subscriber', {})
-        subscriber = Subscriber(
-            successUri=subscriber_dict.get('successUri'),
-            inProgressUri=subscriber_dict.get('inProgressUri'),
-            failedUri=subscriber_dict.get('failedUri'),
-        )
+        subscriber = None
+        subscriber_dict = data.get('subscriber')
+        if subscriber_dict:
+            try:
+                success_uri = subscriber_dict['successUri']
+            except KeyError:
+                return self.get_exception(
+                    HTTPStatus.BAD_REQUEST, headers, request.format,
+                    'MissingParameterValue', 'Missing successUri')
+            else:
+                subscriber = Subscriber(
+                    # NOTE: successUri is mandatory according to the standard
+                    successUri=success_uri,
+                    inProgressUri=subscriber_dict.get('inProgressUri'),
+                    failedUri=subscriber_dict.get('failedUri'),
+                )
 
         try:
             execution_mode = RequestedProcessExecutionMode(

pygeoapi/process/manager/base.py

@@ -289,7 +289,7 @@ def _execute_handler_sync(self, p: BaseProcessor, job_id: str,
 
             self.update_job(job_id, job_update_metadata)
 
-            if subscriber and subscriber.successUri:
+            if subscriber:
                 response = requests.post(subscriber.successUri, json=outputs)
                 LOGGER.debug(
                     f'Success notification response: {response.status_code}'

pygeoapi/util.py

@@ -597,7 +597,7 @@ class Subscriber:
 
     https://schemas.opengis.net/ogcapi/processes/part1/1.0/openapi/schemas/subscriber.yaml  # noqa
     """
-    successUri: Optional[str]
+    successUri: str
     inProgressUri: Optional[str]
     failedUri: Optional[str]