Breaking up is hard to do, but pouring your heart out on paper is rather awkward. There is really no need for any other information in your resignation letter (including a reason __ which is completely optional). No effusive template and formatting effort is required. This is not a letter that is going to be hanging on anyone's wall, and it probably won't even be filed away!
Otherwise, look to the history of your company. How have your boss and other managers handled employees' resignations? If you see a pattern of upper management refusing to let the team members work out their notice, you can likely expect the same.