This is required because when we add an app extension to the
project, there will be two PRODUCT_BUNDLE_IDENTIFIER fields
in our project file, so we cannot use xcconfig to set that
key directly.
This is so that other developers can work on this codebase
by copying Developer.xcconfig.template to Developer.xcconfig
and setting the DEVELOPMENT_TEAM to their respective Team IDs.
The Team IDs need not be checked into source control.
Roopesh Chander