Manage libdnf5 configuration.

Subcommands:
addrepo      Add repositories from the specified configuration file
             or create a new repository using user options
setopt       Set configuration and repositories options
unsetopt     Uset/remove configuration and repositories options
setvar       Set variables
unsetvar     Unset/remove variables

Note:
Main configuration:
libdnf5 reads the distribution configuration from the drop-in directory
("/usr/share/dnf5/libdnf.conf.d") and system configuration from drop-in
directory ("/etc/dnf/libdnf5.conf.d"). Last, it loads the system
configuration file (by default "/etc/dnf/dnf.conf"). The latter has
the highest priority and is modified by config-manager.

Repository configuration:
Libdnf5 loads the repositories configuration and then loads the configuration
overrides. Configuration overrides are stored in files in
the "/usr/share/dnf5/repos.override.d" and "/etc/dnf/repos.override.d"
directories. The files are sorted alphabetically. The override from the next
file overrides the previous one - the last override value wins.
The config-manager writes the repositories configuration changes to the file
"/etc/dnf/repos.override.d/99-config-manager.repo".

New option:
--create-missing-dir - Allow to create missing directories

Without this option, an exception is thrown if the directory is missing.

What happens when the destination repository configuration file already
exists?
By default throw an error.

--overwrite  - Allow overwriting of existing repository configuration file

--add-or-replace - Allow adding or replacing a repository in the existing
                   configuration file