[Alerting]: alertmanager notifier fixes (#34575) (#34589)

(cherry picked from commit b48832c0f7)

Co-authored-by: Sofia Papagiannaki <papagian@users.noreply.github.com>

pkg/services/ngalert/notifier/alertmanager.go

@@ -442,6 +442,8 @@ func (am *Alertmanager) buildReceiverIntegrations(receiver *apimodels.PostableAp
 			n, err = channels.NewThreemaNotifier(cfg, tmpl)
 		case "opsgenie":
 			n, err = channels.NewOpsgenieNotifier(cfg, tmpl)
+		case "prometheus-alertmanager":
+			n, err = channels.NewAlertmanagerNotifier(cfg, tmpl)
 		default:
 			return nil, fmt.Errorf("notifier %s is not supported", r.Type)
 		}

pkg/services/ngalert/notifier/available_channels.go

@@ -638,7 +638,7 @@ func GetAvailableNotifiers() []*alerting.NotifierPlugin {
 			},
 		},
 		{
-			Type:        "alertmanager",
+			Type:        "prometheus-alertmanager",
 			Name:        "Alertmanager",
 			Description: "Sends notifications to Alertmanager",
 			Heading:     "Alertmanager Settings",
@@ -651,6 +651,19 @@ func GetAvailableNotifiers() []*alerting.NotifierPlugin {
 					PropertyName: "url",
 					Required:     true,
 				},
+				{
+					Label:        "Basic Auth User",
+					Element:      alerting.ElementTypeInput,
+					InputType:    alerting.InputTypeText,
+					PropertyName: "basicAuthUser",
+				},
+				{
+					Label:        "Basic Auth Password",
+					Element:      alerting.ElementTypeInput,
+					InputType:    alerting.InputTypePassword,
+					PropertyName: "basicAuthPassword",
+					Secure:       true,
+				},
 			},
 		},
 		{