Adds support for dot-prefixed paths in git

- in `flux bootstrap` and `flux create kustomization` etc.
- E.g. for example `--path=.flux` should work now
- Previous behaviour is to strip off any leading "." and leave you with
  "./flux" in the kustomizations / folder structure generated by `flux
  bootstrap`

Signed-off-by: Simon Howe <footless@gmail.com>

internal/flags/safe_relative_path.go

@@ -41,7 +41,10 @@ func (p *SafeRelativePath) Set(str string) error {
 		return fmt.Errorf("invalid relative path '%s': %w", cleanP, err)
 	}
 	// NB: required, as a secure join of "./" will result in "."
-	cleanP = fmt.Sprintf("./%s", strings.TrimPrefix(cleanP, "."))
+	if cleanP == "." {
+		cleanP = ""
+	}
+	cleanP = fmt.Sprintf("./%s", cleanP)
 	*p = SafeRelativePath(cleanP)
 	return nil
 }