nixos/logrotate: allow sending signal to arbitrary processes

Various postrotate scripts send e.g. SIGHUP to processes, to have them
reload their config or reopen their logfile.

nixos/modules/services/logging/logrotate.nix

@@ -261,6 +261,7 @@ in
  CapabilityBoundingSet = [
  "CAP_CHOWN"
  "CAP_DAC_OVERRIDE"
+ "CAP_KILL"
  "CAP_SETUID"
  "CAP_SETGID"
  ];