statuspage: Properly detect the update is for component or incident.

The value of "status_indicator" can be "none" for both the component
and incident updates[1]. Also, it is not at all necessary that the value of
"status_indicator" is always "none" for incident updates[2][3]. So our previous
logic of using the value of "status_indicator" to determine whether
the update is that of a component or incident was incorrect. Instead, we
should use "incident" or "component" keys to determine the type of update.

This commit fixes issues [1] and [2] in sentry.

1. https://sentry.io/organizations/zulip/issues/2303217561
2. https://sentry.io/organizations/zulip/issues/2303197407
3. https://support.atlassian.com/statuspage/docs/enable-webhook-notifications/

zerver/webhooks/statuspage/fixtures/incident_created.json

@@ -6,7 +6,7 @@
     },
     "page": {
         "id": "jb7j80lkgqvb",
-        "status_indicator": "none",
+        "status_indicator": "critical",
         "status_description": "All Systems Operational"
     },
     "incident": {

zerver/webhooks/statuspage/view.py

@@ -4,6 +4,7 @@ from typing import Any, Dict
 from django.http import HttpRequest, HttpResponse
 
 from zerver.decorator import REQ, has_request_variables, webhook_view
+from zerver.lib.exceptions import UnsupportedWebhookEventType
 from zerver.lib.response import json_success
 from zerver.lib.webhooks.common import check_send_webhook_message
 from zerver.models import UserProfile
@@ -57,14 +58,14 @@ def api_statuspage_webhook(
     payload: Dict[str, Any] = REQ(argument_type="body"),
 ) -> HttpResponse:
 
-    status = payload["page"]["status_indicator"]
-
-    if status == "none":
+    if "incident" in payload:
         topic = get_incident_topic(payload)
         body = get_incident_events_body(payload)
-    else:
+    elif "component" in payload:
         topic = get_component_topic(payload)
         body = get_components_update_body(payload)
+    else:
+        raise UnsupportedWebhookEventType("unknown-event")
 
     check_send_webhook_message(request, user_profile, topic, body)
     return json_success()