acct-group/dhcp acct-user/dhcp: Add stub for dhcp group and user.

BUG=b/223987299
TEST=presubmit
RELEASE_NOTE=None

Change-Id: Ide7e765ee9a1395be4120c47b3293a41b4da89e6
Reviewed-on: https://cos-review.googlesource.com/c/third_party/overlays/eclass-overlay/+/30864
Tested-by: Cusky Presubmit Bot <presubmit@cos-infra-prod.iam.gserviceaccount.com>
Reviewed-by: Robert Kolchmeyer <rkolchmeyer@google.com>