Add methods to config.New().Paths for site and distribution overlays

- SiteOverlaySourcedir() uses WWOverlaydir (/var/lib/warewulf/overlays)
- DistributionOverlaySourcedir() uses Datadir (/usr/share/warewulf/overlays)
- config.New().Warewulf.DataStore moved to config.New().Paths.Datadir
- FindOverlays() ignores missing distribution overlay directory

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

internal/app/wwctl/power/reset/root_test.go

@@ -28,7 +28,7 @@ nodes:
     - default
     ipmi:
       ipaddr: 10.10.10.10`)
-	env.ImportFile(t, "share/warewulf/bmc/ipmitool.tmpl", "../../../../../lib/warewulf/bmc/ipmitool.tmpl")
+	env.ImportFile(t, "usr/share/warewulf/bmc/ipmitool.tmpl", "../../../../../lib/warewulf/bmc/ipmitool.tmpl")
 
 	tests := map[string]struct {
 		args     []string