For projects with several application targets and extension targets，
we add extension target as dependencies to application target，
but we may want extension target（eg Share Extension）use different Configs（eg 'PRODUCT_BUNDLE_IDENTIFIER'）when embed in differernt application targets.
because application targets may have different identifiers，and "If an app contains an app extension, the app extension’s bundle identifier must be prefixed by the app’s bundle identifier."

How to accomplish this ? Any tips and examples are appreciated.