create docker system user, refactor docker

Signed-off-by: ahuston-0 <aliceghuston@gmail.com>

systems/palatine-hill/docker.nix

@@ -0,0 +1,11 @@
+{ ... }:
+
+{
+  virtualisation.docker.daemon.settings.data-root = "/var/lib/docker2";
+
+  users.users.docker-service = {
+    isSystemUser = true;
+    extraGroups = [ "docker" ];
+    uid = 600;
+  };
+}