add a preview note for all non-bootstrap commands

Signed-off-by: Sanskar Jaiswal <jaiswalsanskar078@gmail.com>

cmd/flux/main.go

@@ -224,3 +224,10 @@ func readPasswordFromStdin(prompt string) (string, error) {
 	fmt.Println()
 	return strings.TrimRight(out, "\r\n"), nil
 }
+
+func withPreviewNote(desc string) string {
+	previewNote := `⚠️  Please note that this command is in preview and under development.
+While we try our best to not introduce breaking changes, they may occur when
+we adapt to new features and/or find better ways to facilitate what it does.`
+	return fmt.Sprintf("%s\n\n%s", strings.TrimSpace(desc), previewNote)
+}