Control availability of extensions unpublished on the Chrome Web Store.

If this policy is enabled, extensions that are unpublished on the Chrome Web Store will be disabled in Brave. This policy only applies to extensions that are installed and updated from the Chrome Web Store. Off-store extensions such as unpacked extensions installed using developer mode and extensions installed using the command-line switch are ignored. Force-installed extensions that are self-hosted are ignored. All version-pinned extensions are also ignored. If the policy is set to AllowUnpublished (0) or not set, extensions that are unpublished on the Chrome Web Store are allowed. If the policy is set to DisableUnpublished (1), extensions that are unpublished on the Chrome Web Store are disabled.