No plugin or API for automatically discovering and loading repositories from removable media (e.g. install DVD repositories)

[Conan-Kudo]

I discovered as a byproduct of triaging rhbz#2437410 that dnf5 cannot automatically discover and load repositories on removable media (such as USB sticks or DVDs). This is particularly problematic with airgapped environments where it is common to shuffle repositories around on WORM media such as CDs and DVDs.

I'm not sure it makes sense to have this as a core API like it was in the libdnf context API, but it probably makes sense to have it as a libdnf5 plugin so that it activates and configures on-demand depending on mounted media.

[ppisar]

C libdnf code used by PackageKit https://github.com/rpm-software-management/libdnf/blob/ac318b2a1aaa4368ac6c266186ec9c7b6bf8fb1c/libdnf/dnf-repo-loader.cpp#L462-L464.