fix(api): sort upstreams in the API response

internal/alertmanager/upstream.go

@@ -4,6 +4,7 @@ import (
 	"fmt"
 	"net/http"
 	"net/url"
+	"sort"
 	"sync"
 	"time"
 
@@ -82,6 +83,9 @@ func GetAlertmanagers() []*Alertmanager {
 	for _, am := range upstreams {
 		ams = append(ams, am)
 	}
+	sort.Slice(ams[:], func(i, j int) bool {
+		return ams[i].Name < ams[j].Name
+	})
 	return ams
 }