Add flag for migration of MTE policy to DPE

First part of the work to migrate MTE policy from ActiveAdmin to
DevicePolicyEngine.

Test: N/A - adding a flag.
Bug: 376213673
Flag: EXEMPT only adding a new flag
Change-Id: Iea4f58cf65eb172fbd5222cf148f7d5f5be0bd0c
1 file changed