nixos/journalbeat: Add a loose dependency on elasticsearch

Avoid unnecssary back-off when elasticsearch is running on the same
host.

nixos/modules/services/logging/journalbeat.nix

@@ -88,6 +88,8 @@ in
     systemd.services.journalbeat = {
       description = "Journalbeat log shipper";
       wantedBy = [ "multi-user.target" ];
+      wants = [ "elasticsearch.service" ];
+      after = [ "elasticsearch.service" ];
       preStart = ''
         mkdir -p ${cfg.stateDir}/data
         mkdir -p ${cfg.stateDir}/logs