Change image provision directory to "images"

Previous name (before #1641) was "container." New name (from #1641) was "image"
but a plural name seems better.

Signed-off-by: Jonathon Anderson <janderson@ciq.com>

internal/pkg/image/config.go

@@ -25,7 +25,7 @@ func RunDir(name string) string {
 
 func ImageParentDir() string {
 	conf := warewulfconf.Get()
-	return path.Join(conf.Paths.WWProvisiondir, "image")
+	return path.Join(conf.Paths.WWProvisiondir, "images")
 }
 
 func ImageFile(name string) string {