Override help subcommand logic

I am using cobra. I don't need subcommands. I do want the default help and completion subcommands to be generated. There should be an option for "generate default subcommands even if no other subcommands are defined".

```go
func (c *Command) InitDefaultHelpCmd() {
	if !c.HasSubCommands() {
		return
	}
	// ...
}

There should be some option that disables the subcommand check.