Search - add support for saving the UserId in the Index - part 2

- get UserId for remote SearchIndexablesProvider and put it into
the Index too

This CL depends on that Framework CL: a0791edf01524be7c9ae819b11c05e8191a97ded

See bug: ##15837747 Search - update for Enterprise support

Change-Id: I47789aa02545bbacc68468cabfb32a253003ec5b