Bug 1630418 support pkcs11 as an optional extension permission r=rpl

Differential Revision: https://phabricator.services.mozilla.com/D71123

browser/components/extensions/schemas/pkcs11.json

@@ -3,7 +3,7 @@
     "namespace": "manifest",
     "types": [
       {
-        "$extend": "Permission",
+        "$extend": "OptionalPermission",
         "choices": [{
           "type": "string",
           "enum": [