Alerting: Update remote alertmanager to use extended receivers API. (#89253)

* Alerting: Update remote alertmanager to use extended receivers API.

* Update integration test and Mimir image

* Update Mimir image in more places

pkg/services/ngalert/remote/client/alertmanager_configuration.go

@@ -11,7 +11,8 @@ import (
 )
 
 const (
-	grafanaAlertmanagerConfigPath = "/api/v1/grafana/config"
+	grafanaAlertmanagerConfigPath    = "/api/v1/grafana/config"
+	grafanaAlertmanagerReceiversPath = "/api/v1/grafana/receivers"
 )
 
 type UserGrafanaConfig struct {
@@ -63,3 +64,16 @@ func (mc *Mimir) CreateGrafanaAlertmanagerConfig(ctx context.Context, cfg *apimo
 func (mc *Mimir) DeleteGrafanaAlertmanagerConfig(ctx context.Context) error {
 	return mc.doOK(ctx, grafanaAlertmanagerConfigPath, http.MethodDelete, nil)
 }
+
+func (mc *Mimir) GetReceivers(ctx context.Context) ([]apimodels.Receiver, error) {
+	response := []apimodels.Receiver{}
+
+	// nolint:bodyclose
+	// closed within `do`
+	_, err := mc.do(ctx, grafanaAlertmanagerReceiversPath, http.MethodGet, nil, &response)
+	if err != nil {
+		return nil, err
+	}
+
+	return response, nil
+}

pkg/services/ngalert/remote/client/mimir.go

@@ -29,6 +29,9 @@ type MimirClient interface {
 	DeleteGrafanaAlertmanagerConfig(ctx context.Context) error
 
 	ShouldPromoteConfig() bool
+
+	// Mimir implements an extended version of the receivers API under a different path.
+	GetReceivers(ctx context.Context) ([]apimodels.Receiver, error)
 }
 
 type Mimir struct {