acct-group/dhcp acct-user/dhcp: Add stub for dhcp group and user. BUG=b/223987141 TEST=presubmit RELEASE_NOTE=None cos-patch: lts-refresh 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> (cherry picked from commit d2c1f0967b1b06b02fb9b3cefd8528469bc7d3e7) Reviewed-on: https://cos-review.googlesource.com/c/third_party/overlays/eclass-overlay/+/30960