keep the memberlist labels jsonnet config backwards compatible with 2.6.1 (#6711)
keep the memberlist labels jsonnet config backwards compatible with 2.6.1 (#6711)

* keep the memberlist labels jsonnet config backwards compatible with 2.6.1

* fix comment
grafana/loki,grafana/loki,grafana/loki,grafana/loki,grafana/loki,grafana/loki