Move PersistentDataBlock* in server to its namespace

Previous automerge was skipped by mistake

Also add OWNERS.

Bug: 303523453
Test: m
Test: mma in services/devicepolicy/ services/tests/servicestests/
(cherry picked from https://android-review.googlesource.com/q/commit:d34869871fe5df392d97a80ffb34d52b9bda7384)
Change-Id: I5c63ba2e56a7d104c0f7b5758058730aed0a237c