Add flag to control implementation of all private space features

We are adding a new feature flag to control the implementation of all
privte space features. The allow_private_profile flag was earlier used
for this purpose. However, we plan to separate out the API changes
behind a separate flag. We intend to use the allow_private_profile flag
as a mean to flag guard the API changes, while this new flag will now be
the global control for all the features.

Bug: 299069460
Test: m all_aconfig_declarations
Change-Id: Icd6287a236bc596f3e5bbe05d7986055766d1a74