...but still allow for setting `dataDir` to a custom path. This gets rid of the use of the deprecated option PermissionsStartOnly. Also, add the ability to customize user and group, since that could be useful with a custom `dataDir`.
*** NixOS *** NixOS is a Linux distribution based on the purely functional package management system Nix. More information can be found at https://nixos.org/nixos and in the manual in doc/manual.