fix(migrators/goose): read from filesytem if no FS

[dmksnnk]

This CR should allow to read migrations folder from parent directory like ../migrations.

I have a migrations directory in the root of the project, so to make migrations work, I need to provide FS with root directory:

root, err := filepath.Abs("../../../..")
if err != nil {
  t.Fatal("get abs path", err)
}

migrator := goosemigrator.New("migrations", goosemigrator.WithFS(os.DirFS(root)))

This CR should allow to do just:

migrator := goosemigrator.New("../../../../migrations")

Also, golangmigrator does not have fs.FS by default too.