Add retrieveBugreport API

Adds API support for deferring consent while
generating a bugreport, along with support for
the same caller to retrieve a bugreport that
was previously generated by them.

Test: atest CtsRootBugreportTestCases
Test: atest BugreportManagerServiceImplTest
Bug: 245328405
Change-Id: I6ea42fdc3609344aad3126c7af0a6f32666e7438