Pass in Alerta authentication details for Alertmanager to send alerts with

Related-PROD: PROD-35884 PROD-35932 PROD-35958
Change-Id: I2bea5ef751883cd266139539fec1f7bde96a0ea0
diff --git a/prometheus/alertmanager/notification/alerta.yml b/prometheus/alertmanager/notification/alerta.yml
index 2ab3509..729aa26 100644
--- a/prometheus/alertmanager/notification/alerta.yml
+++ b/prometheus/alertmanager/notification/alerta.yml
@@ -16,9 +16,5 @@
             enabled: true
             webhook_configs:
               alerta:
-                url: "http://${_param:alertmanager_notification_alerta_host}:${_param:alertmanager_notification_alerta_port}/api/webhooks/prometheus"
+                url: "http://${_param:alertmanager_notification_alerta_host}:${_param:alertmanager_notification_alerta_port}/api/webhooks/prometheus?api-key=${_param:alerta_admin_key}"
                 send_resolved: true
-                http_config:
-                  basic_auth:
-                    username: "${_param:alerta_admin_username}"
-                    password: "${_param:alerta_admin_password}"