spec: Provide dnf4 by python3-dnf

To differentiate from DNF5, python3-dnf already packages /usr/bin/dnf4
symbolic link. After dnf5 obsoleting dnf, people willing to install
DNF4 they had to install python3-dnf package, a package whose name is
hard to remember.

This patch adds "dnf4" RPM provide to python3-dnf package.

This patch should be backported to all systems so that people can rely
on this new identifier.

Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=2328463

dnf.spec

@@ -153,6 +153,7 @@ Requires:       rpm-plugin-systemd-inhibit
 %else
 Recommends:     (rpm-plugin-systemd-inhibit if systemd)
 %endif
+Provides:       dnf4 = %{version}-%{release}
 Provides:       dnf-command(alias)
 Provides:       dnf-command(autoremove)
 Provides:       dnf-command(check-update)