needs-restarting to recommend systemd's soft-reboot if possible

[ppisar]

Systemd 254 added soft-reboot.target https://www.freedesktop.org/software/systemd/man/latest/systemd-soft-reboot.service.html which can be used for terminating all user-space processes, reexecuting systemd and starting user-space daemons as is done in a normal reboot after switching from initramfs to a real root file system.

This is a request for enhancing needs-restarting plugin to move glibc, systemd, dbus, dbus-broker, and dbus-daemon from NEED_REBOOT list:

 NEED_REBOOT = ['kernel', 'kernel-core', 'kernel-rt', 'glibc',
               'linux-firmware', 'systemd', 'dbus', 'dbus-broker',
               'dbus-daemon', 'microcode_ctl']

into a new list not pertaining firmware and kernel space. If needs-restarting determines that only packages from the new list are affected, needs-restarting --reboothint will recommend to soft reboot instead of standard reboot.

Now the command reports:

# needs-restarting --reboothint
Core libraries or services have been updated since boot-up:
  * glibc

Reboot is required to fully utilize these updates.
More information: https://access.redhat.com/solutions/27943

After implementing this feature request it would report:

# needs-restarting --reboothint
Core libraries or services have been updated since boot-up:
  * glibc

Soft reboot is required to fully utilize these updates.
More information: https://access.redhat.com/solutions/27943

Downstream request: https://issues.redhat.com/browse/RHEL-138472