Allow ptrace to any process of the same user

Allows users to attach GDB to their own processes, without requiring
running the program with GDB from the start. It is only available in
compute nodes, the storage nodes continue with the restricted settings.

Reviewed-by: Aleix Boné <abonerib@bsc.es>

m/common/base/boot.nix

@@ -19,6 +19,10 @@
 
   boot.kernel.sysctl = {
     "kernel.perf_event_paranoid" = lib.mkDefault "-1";
+
+    # Allow ptracing (i.e. attach with GDB) any process of the same user, see:
+    # https://www.kernel.org/doc/Documentation/security/Yama.txt
+    "kernel.yama.ptrace_scope" = "0";
   };
 
   boot.kernelPackages = pkgs.linuxPackages_latest;