Alerting: Comprehensive payload for Alertmanager convert API tests (#110485)

* do not remove global config
* create more comprehensive payload for mimir alertmanager testing

pkg/services/ngalert/api/api_convert_prometheus_test.go

@@ -1992,6 +1992,19 @@ receivers:
 		require.Equal(t, http.StatusOK, response.Status())
 
 		expectedResponse := `alertmanager_config: |
+  global:
+      resolve_timeout: 5m
+      http_config:
+          follow_redirects: true
+          enable_http2: true
+      smtp_hello: localhost
+      smtp_require_tls: true
+      pagerduty_url: https://events.pagerduty.com/v2/enqueue
+      opsgenie_api_url: https://api.opsgenie.com/
+      wechat_api_url: https://qyapi.weixin.qq.com/cgi-bin/
+      victorops_api_url: https://alert.victorops.com/integrations/generic/20131114/alert/
+      telegram_api_url: https://api.telegram.org
+      webex_api_url: https://webexapis.com/v1/messages
   route:
       receiver: webhook
       continue: false