filesystem_deploy_action: add option for kernel parameters
filesystem_deploy_action: add option for kernel parameters

Additional option 'append-kernel-cmdline' as we have for
'ostree-deploy' allows to fill `/etc/kernel/cmdline` config
with custom boot parameters.

Signed-off-by: Denis Pynkin <3fbf95ee68899518ee8799d35f88c8f7982aa936@collabora.com>
Fixes: #47

go-debos/debos,d4s/debos