Ensure postgresql starts before test tracking service

nixos.nix

@@ -24,6 +24,8 @@ let
     systemd.services.gitlab-test-tracking = {
       serviceConfig.User = "ghc-test-tracking";
       description = "GitLab test tracking service";
+      before = [ "postgresql.service" ];
+      requires = [ "postgresql.service" ];
       script = ''
         ${service}/bin/gitlab-test-tracking-service \
           --gitlab-root=https://gitlab.${config.ghc.rootDomain} \