Changes

{open5gs,osmo-uecups}-latest: don't hardcode UID

Adjust open5gs-latest and osmo-uecups-latest to not hardcode a UID. This
is in preparation for creating a "build" user in
debian-bookworm-obs-latest, like we have it in debian-bookworm-build.

Change-Id: Icaebf46487056cea745805527fdc545d9a1846cd

debian-bookworm-obs-latest: add build user

Copy the block for configuring the build user and disabling man pages
from debian-bookworm-build. This fixes failures on
ttcn3-ggsn-test-kernel-latest* (non-latest worked fine since these use
containers based on debian-bookworm-build).

Fixes: 5a48bfbe ("scripts/kernel-test: build initrd+kernel as user")
Change-Id: Idee29d5b9796e8905bdf822d076f25612cbc77a0