Update the recovery grub boot config to allow all system labels that are
considered valid by snapd, which are typically just numbers based on date, eg.
20210706 but follow the same rules as model names so hyphen separated
numbers/letters are allowed.
Signed-off-by: Maciej Borzecki <maciej.zenon.borzecki@canonical.com>
Add support for snapd_full_cmdline_args variable that carries a set of command
line arguments that shall be used in place of the static and extra ones. Thus
the contents of the new variable effectively become the list of arguments that
directly follows `snapd_recovery_mode=.. snapd_recovery_system=...` in the
kernel command line passed by grub.
The boot config edition is not bumped yet, thus it will not trigger an automatic
boot config update when a new snapd gets installed.
Signed-off-by: Maciej Borzecki <maciej.zenon.borzecki@canonical.com>
