Alerting: Implement /status for the notification system (#33227)

* Alerting: Implement /status for the notification system

Implements the necessary plumbing to have a /status endpoint on the
notification system.

* Add API examples

* Update API specs

* Update prometheus/common dependency

Co-authored-by: Sofia Papagiannaki <sofia@grafana.com>

pkg/services/ngalert/api/test-data/am-alertmanager-recipient.http

@@ -96,6 +96,10 @@ content-type: application/json
 # get AM alerts
 GET http://admin:admin@localhost:3000/api/alertmanager/{{alertManagerDatasourceID}}/api/v2/alerts
 
+###
+# get status
+GET http://admin:admin@localhost:3000/api/alertmanager/{{alertManagerDatasourceID}}/api/v2/status
+
 ###
 # get AM alert groups
 GET http://admin:admin@localhost:3000/alertmanager/{{alertManagerDatasourceID}}/api/v2/alerts/groups

pkg/services/ngalert/api/test-data/am-grafana-recipient.http

@@ -21,6 +21,14 @@ DELETE http://admin:admin@localhost:3000/api/alertmanager/{{grafana}}/config/api
 POST http://admin:admin@localhost:3000/api/alertmanager/{{grafana}}/api/v2/alerts
 content-type: application/json
 
+###
+# get AM alerts
+GET http://admin:admin@localhost:3000/api/alertmanager/{{grafana}}/api/v2/alerts
+
+###
+# get AM status
+GET http://admin:admin@localhost:3000/api/alertmanager/{{grafana}}/api/v2/status
+
 ###
 # get silences - no silences
 GET http://admin:admin@localhost:3000/api/alertmanager/{{grafana}}/api/v2/silences?Filter=foo="bar"&Filter=bar="foo"