nixos/apparmor: allow reloading profiles without losing confinement

Define ExecReload, otherwise reload implies stop followed by start, which
leaves existing processes in unconfined state [1].

[1]: https://gitlab.com/apparmor/apparmor/wikis/AppArmorInSystemd

nixos/modules/security/apparmor.nix

@@ -48,6 +48,9 @@ in
          ExecStop = map (p:
            ''${pkgs.apparmor-parser}/bin/apparmor_parser -Rv "${p}"''
          ) cfg.profiles;
+         ExecReload = map (p:
+           ''${pkgs.apparmor-parser}/bin/apparmor_parser --reload ${paths} "${p}"''
+         ) cfg.profiles;
        };
      };
    };