Allow default search provider context menu search access

Enables the use of a default search provider on the context menu. If you disable this policy, the search context menu item that relies on your default search provider and sidebar search isn't available. If you enable or don't configure this policy, the context menu item for your default search provider and sidebar search is available. The policy value is only applied when the 'DefaultSearchProviderEnabled' (Enable the default search provider) policy is enabled, and isn't applicable otherwise.