Add OWNERS file for EnforcePermission

This directory will hosts end-to-end tests for @EnforcePermission.
Considered alternative location:
- core/tests/coretests (FrameworksCoreTests): broad ownership, see
  b/243401782.
- system/tools/aidl: our integration tests already exist there. The
  current tests setup for aidl does not install APKs but only raw jar
  files. We want to install a regular application to test the
  effective permissions.

The end-to-end tests will eventually be executed in presubmit via
TEST_MAPPING.

Bug: 269721152
Test: n/a
Change-Id: I6a87b50e794fc3a0ba7c8a48ef9f92b7d6ad5180