nixos/ipfs: do not leak config to journal on startup

The preStart script for the IPFS service will print parts of the configuration
to stdout (and therefore, the journal) when applying profiles on startup. This
may lead to unwanted disclosure of private information, such as remote pinning
service API keys. Fix by sending stdout to /dev/null.

nixos/modules/services/network-filesystems/ipfs.nix

@@ -257,7 +257,7 @@ in
       '' + optionalString cfg.autoMigrate ''
         ${pkgs.ipfs-migrator}/bin/fs-repo-migrations -to '${cfg.package.repoVersion}' -y
       '' + ''
-          ipfs --offline config profile apply ${profile}
+          ipfs --offline config profile apply ${profile} >/dev/null
         fi
       '' + optionalString cfg.autoMount ''
         ipfs --offline config Mounts.FuseAllowOther --json true