Introduce 'dataExtractionRules' manifest attribute

Introduce the attribute apps targeting Android S+ can use to point to an
XML file that contains rules for copying app data during backup and
transfer operations. If this attribute is specified, the config pointed
to by the existing 'fullBackupContent' will be ignored.

Bug: 174216309
Test: m -j
Change-Id: I6ad57a24b40cf5b80b312c719747e8ba89aa0a93