Motivation:
Currently, when setting the default boot pattern, boot assessment status
is not taken into account. This means that with boot assessment enabled,
when an explicit boot entry is configured as the default entry using an
EFI var, as is common for instance in A/B boot schemes, the configured
entry will be booted indefinitly, regardless of the entry's boot
assessment status.
In order to allow for this use case in combination with boot assessment,
we introduce a new `preferred` keyword, both in the config file and in the
bootctl CLI, that acts very similar to the existing `default` keyword but
takes boot assessment into account and never selects any entries that
have been marked as bad.
If the preferred pattern does not resolve to any bootable entry, and a
default pattern is also specified, then the default pattern will be
considered next, and we may then still select a known-bad entry to be
booted.
Fixes: https://github.com/systemd/systemd/issues/31215
Fixes: https://github.com/systemd/systemd/issues/40192
450e0dce02
