fedora: add dbus-broker to coreos-installer dracut modules

With the sources update, the iot-simplified-installer in Fedora 40
started failing in the dracut stage with:

    dracut[I]: Module 'dbus-daemon' will not be installed, because command 'dbus-daemon' could not be found!
    dracut[E]: Module 'dbus' depends on 'dbus-daemon', which can't be installed
    dracut[E]: Module 'network-manager' depends on 'dbus', which can't be installed
    ...

I'm not entirely sure what caused this change.  I suspect it's related
to this change (which is included in dracut 060 in Fedora 40):
dracutdevs/dracut@3f8f115

The dbus dracut module has a dependency on either dbus-daemon or
dbus-broker.  Simply installing dbus-broker isn't enough though (it's
already in the simplified-installer package set).

Enabling the dbus-broker module explicitly fixes the issue.

(Sidenote: Installing dbus-daemon *does* solve the issue though, which I
also found strange)

pkg/manifest/coreos_installer.go

@@ -187,6 +187,7 @@ func (p *CoreOSInstaller) serialize() osbuild.Pipeline {
 		p.AdditionalDracutModules,
 		"coreos-installer",
 		"fdo",
+		"dbus-broker",
 	)
 
 	dracutStageOptions := dracutStageOptions(p.kernelVer, p.Biosdevname, dracutModules)