Let's make it possible to "suggest" that certain features or components
are enabled under some conditions.
For this, both features and components gain two things:
1. A Suggested= field which takes a boolean. If true the
feature/component will be suggested for installation, if false it
will not.
2. A set of SuggestedOnXYZ= settings are modelled after ConditionXYZ= in
unit files (and implement a subset of them), will suggest some
component/feature under specific conditions.
The result of the condition is shown in the various output tools.
Optional features allow distros to define sets of transfers that can
be enabled or disabled by the system administrator. This is useful for
situations where a distro may want to ship some resources version-locked
to the core OS, but many people have no need for the resource, such as:
development tools/compilers, drivers for specialized hardware, language
packs, etc
We also rename sysupdate.d/*.conf -> sysupdate.d/*.transfer, because
now there are more than one type of definition in sysupdate.d/. For
backwards compat, we still load *.conf files as long as no *.transfer
files are found and the *.conf files don't try to declare themselves
as part of any features
Fixes https://github.com/systemd/systemd/issues/33343
Fixes https://github.com/systemd/systemd/issues/33344
Lennart Poettering
Lennart Poettering
Zbigniew Jędrzejewski-Szmek
Matthias Lisin
Adrian Vovk