Add ppAuthCertExt to custom_extensions

The custom_extensions method allows certificate extensions to be access in a manifest.
PUP-6258 introduced a new OID that was never added to the custom_extensions method.
This is causing what is documented here.

You can access certificate extensions in manifests as $trusted["extensions"]["<EXTENSION OID>"].

Select OIDs in the ppRegCertExt and ppAuthCertExt ranges.

The current state has it ppRegCertExt can access in the manifest $trusted['extension'], but not ppAuthCertExt.