systemd: add udev-bash-completion package

systemd: add udev-bash-completion package

Move the 'udevadm' autocompletion script into a dedicated package.
Indeed, bash (and therefore, the bash-completion package) is not
always installed. But the 'udevadm' autocompletion script remains
in ${datadir}/bash-completion.

Creating a dedicated package allows better split, and avoids
installing it if the bash-completion package is missing.

Signed-off-by: Corentin Guillevic <corentin.guillevic@smile.fr>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>