playbook: debian{9,10}: Install/upgrade linux-headers as well
In addition to linux-image we have to explicitly install/upgrade kernel headers as well because once they are installed via nxd-fuse-dkms -> dkms -> linux-headers-amd64, they won't be upgraded, and if linux-image-amd64 gets upgraded, but headers are not, nxd-fuse-dkms will be skipped to recompile for upgraded kernel.
https://lab.nexedi.com/nexedi/slapos.package/merge_requests/133#note_121068