Extend flux migrate to work with local files

Signed-off-by: Matheus Pimenta <matheuscscp@gmail.com>

cmd/flux/testdata/migrate/file-system/dir.golden/some-file.yml

@@ -0,0 +1,17 @@
+# This file has Windows line endings.
+
+apiVersion: image.toolkit.fluxcd.io/v1
+kind: ImageRepository
+---
+
+
+
+apiVersion: image.toolkit.fluxcd.io/v1
+kind: ImagePolicy
+
+
+---
+
+apiVersion: image.toolkit.fluxcd.io/v1/v2
+kind: ImagePolicy
+