Move slurm client in a separate module

Reviewed-by: Rodrigo Arias Mallo <rodrigo.arias@bsc.es>

m/hut/slurm-server.nix

@@ -0,0 +1,7 @@
+{ ... }:
+
+{
+  services.slurm = {
+    server.enable = true;
+  };
+}