Add ParterConfigHelper to retrieve customizable resources

Once this arrives in google3.  We will switch to using the Partner class from carsetupwizardlib.  PartnerConfigHelper is only meant for setupwizardlib.  SUW will still use Partner to fetch resource overlay.

Bug: 130542432
Test: CarSetupWizardLibRoboTests
Change-Id: I1826e61e6bbbe7eaff277ceeb276c75618e56366
(cherry picked from commit 9ead1f83a458151102a0ee6fb268949f412187b0)