rootfs: add resize, timesync, and staging repo cleanup

[bjordiscollaku]

Three independent improvements to the rootfs build pipeline:

1. First-boot filesystem resize (rootfs-resize.service)

   • Add Step 7.6 that writes /usr/local/sbin/rootfs-resize.sh and /etc/systemd/system/rootfs-resize.service into the rootfs from the host side before entering chroot.
   • The service uses a ConditionPathExists flag file (/etc/rootfs-resize-pending) to guarantee single execution: on first boot resize2fs expands the ext4 root filesystem to fill the underlying block device, then ExecStartPost removes the flag so the unit never fires again.
   • systemctl enable rootfs-resize.service is called inside the chroot to wire the unit into multi-user.target.

2. Time synchronization (systemd-timesyncd)

   • Install and enable systemd-timesyncd inside the chroot immediately after the networking stack.
   • systemd-timesyncd is the standard lightweight SNTP client shipped with systemd and is the broadly accepted solution on both Ubuntu and Debian for non-server embedded/IoT targets. It resolves clock-skew failures observed in browsers and TLS certificate validation at runtime.

3. Staging apt source cleanup (Step 9.5)

   • Remove /etc/apt/sources.list.d/pkg-oss-staging-repo.list from the rootfs after the chroot exits and before the ext4 image is created, ensuring internal staging repositories do not leak into the shipped image.

[keerthi-go]

Can we create this as static file, or a deb package which can be installed instead of creating it at build time?

[shoudil]

Reg. time sync, should we consider to use chrony instead of systemd-timesyncd
PR: https://github.com/qualcomm-linux/qcom-distro-images/pull/52
Ref: https://en.ubunlog.com/Ubuntu-25-will-adopt-Chrony--says-goodbye-to-Bazaar--and-says-hello-to-Git./