fix: Add missing management.setEnabled

setEnabled is partially implemented in Firefox:
- https://bugzil.la/1282982
- https://developer.mozilla.org/docs/Mozilla/Add-ons/WebExtensions/API/management/setEnabled

The management API has many more methods in Chrome,
Firefox does not support them:
- createAppShortcut
- generateAppForLink
- getPermissionWarningsById
- getPermissionWarningsByManifest
- launchApp
- setLaunchType
- uninstall

api-metadata.json

@@ -333,6 +333,10 @@
       "minArgs": 0,
       "maxArgs": 0
     },
+    "setEnabled": {
+      "minArgs": 2,
+      "maxArgs": 2
+    },
     "uninstallSelf": {
       "minArgs": 0,
       "maxArgs": 1