sysusers: add debug lines to failing getent/putent operations

I'm trying to use systemd-sysusers for systemd.rpm itself, and the invocation
in dnf chroot is failing like this:
...
Creating group input with gid 999.
Creating group kvm with gid 36.
Creating group render with gid 998.
Creating group sgx with gid 997.
Creating group systemd-journal with gid 190.
Creating group systemd-network with gid 192.
Creating user systemd-network (systemd Network Management) with uid 192 and gid 192.
Creating group systemd-oom with gid 996.
Creating user systemd-oom (systemd Userspace OOM Killer) with uid 996 and gid 996.
Creating group systemd-resolve with gid 193.
Creating user systemd-resolve (systemd Resolver) with uid 193 and gid 193.
Creating group systemd-timesync with gid 995.
Creating user systemd-timesync (systemd Time Synchronization) with uid 995 and gid 995.
Creating group systemd-coredump with gid 994.
Creating user systemd-coredump (systemd Core Dumper) with uid 994 and gid 994.
Failed to write files: Function not implemented

Let's add more info to make such failures easier to debug.