Prepare for DNF 5, don't depend on `dnf`

(I'm filing issues with all the packages that currently depend on dnf.)

DNF 5 is a new package manager that will replace DNF 4 in Fedora 39+: Starting in Fedora 39, the dnf command will be provided by the dnf5 package rather than the dnf package, and dnf5 will obsolete dnf. Since fedora-upgrade currently depends on DNF 4, it should choose one of the following strategies to avoid breaking the Fedora upgrade:

Add support for DNF 5, and depend on the dnf5 package in Fedora 39+ instead of dnf. Builds of DNF 5 are available in this COPR repository: https://copr.fedorainfracloud.org/coprs/rpmsoftwaremanagement/dnf5-unstable, and documentation is available here: https://dnf5.readthedocs.io/en/latest/.
Alternatively, or in the meantime, change the fedora-upgrade package to depend on python3-dnf instead of dnf, and call the dnf-3 binary instead of dnf. The old DNF 4 command will still be available in the distribution, but only as dnf-3 (the binary is called dnf-3 rather than dnf4 for historical reasons; it is the "Python 3 version" of DNF). The first option is preferred to this one; it is not recommended to modify installed software using both DNF 4 and DNF 5 on the same system.
Or, if this package is no longer being maintained, consider removing it from Fedora.

At some point, this project should adopt DNF 5, but the immediate issue is removing the dependency on dnf. We are planning to replace DNF with DNF5 in Fedora Rawhide very soon, by 2023-06-01, and the fedora-upgrade package will break as long as it still depends on the dnf package.

For more information about the switch to DNF 5, see https://fedoraproject.org/wiki/Changes/ReplaceDnfWithDnf5.

xsuchy / fedora-upgrade

Prepare for DNF 5, don't depend on `dnf` #44