transmission_4: add option to allow additional paths in AppArmor rules

This change adds an extraAppArmorPaths option to the transmission_4
derivation to allow additional read-only paths to be added to the
ppArmor rules. This can be combined with the TRANSMISSION_WEB_HOME
environment variable to override the web UI.

pkgs/applications/networking/p2p/transmission/4.nix

@@ -35,6 +35,7 @@
 , enableCli ? true
 , installLib ? false
 , apparmorRulesFromClosure
+, extraAppArmorPaths ? []
 }:
 
 stdenv.mkDerivation (finalAttrs: {
@@ -135,6 +136,7 @@ stdenv.mkDerivation (finalAttrs: {
       rwk /tmp/tr_session_id_*,
 
       r $out/share/transmission/public_html/**,
+      ${lib.strings.concatMapStrings (x: "r ${x},\n") extraAppArmorPaths}
 
       include <local/bin.transmission-daemon>
     }