microdnf --installroot requires a bunch of options set that can be set via the config file

[Conan-Kudo]

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Is there a reason why we're forcing a whole bunch of command line options to be set when the config file can do it?

https://github.com/rpm-software-management/microdnf/blob/9edaf509715c74fb25c32f007ee12348453cc478/dnf/dnf-main.c#L437-L444

In the KIWI image builder, we set all these things up through the config file, rather than through options passed to DNF, and I'd like that to work with microdnf by doing microdnf --config=/path/to/file --installroot=/path/to/root ... as it does in DNF.

(cc: @schaefi, @davidcassany)

[Conan-Kudo]

cc: @tabowling