Use rel filepath in auto generated kustomization

This works around another bug on Windows platforms that would cause the
kustomize-controller to choke on the kustomization.yaml generated by the
bootstrap command due to the filepath being in a Windows format.

By using `filepath.Rel`, the output is _just_ the filename for files
relative to the bootstrap path, which is at the moment sufficient to
make it work.

Signed-off-by: Hidde Beydals <hello@hidde.co>

internal/utils/utils.go

@@ -323,7 +323,11 @@ func GenerateKustomizationYaml(dirPath string) error {
 
 		var resources []string
 		for _, file := range files {
-			resources = append(resources, strings.Replace(file, abs, ".", 1))
+			relP, err := filepath.Rel(abs, file)
+			if err != nil {
+				return err
+			}
+			resources = append(resources, relP)
 		}
 
 		kus.Resources = resources