Add organization message usage and service counts to dashboard

- Fetch organization message allowance from API endpoint
- Display messages sent, remaining, and total limit on dashboard
- Add service count statistics (total, live, trial, suspended)
- Pass message usage data to template for chart visualization

app/notify_client/service_api_client.py

@@ -561,6 +561,11 @@ class ServiceAPIClient(NotifyAdminAPIClient):
             url="service/get-service-message-ratio?service_id={0}".format(service_id),
         )
 
+    def get_organization_message_usage(self, org_id):
+        return self.get(
+            url="/organizations/{0}/message-allowance".format(org_id),
+        )
+
 
 service_api_client = ServiceAPIClient()