Add stubs for Kerberos policies

Adds stubs of a couple of policies that will be used to control the
Kerberos functionality for cloud managed Chrome OS devices. The
KerberosEnabled policy is used to guard the feature. No existing
functionality should change if it is disabled (or not defined).

BUG=chromium:952233

Change-Id: I4af3980ad3a94c9a5bfc92bdf8c0a61a8c185726
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1565981
Commit-Queue: Lutz Justen <ljusten@chromium.org>
Reviewed-by: Gabriel Charette <gab@chromium.org>
Reviewed-by: Maksim Ivanov <emaxx@chromium.org>
Cr-Commit-Position: refs/heads/master@{#653548}
10 files changed