Add setting to turn off notification sound

Please add a toggle or just remove the kerching sound from inside the iOS app. I’m not talking about notifications, those are managed from the iOS settings directly as demonstrated by Danny, but this setting does not influence the in-app sound effect that happens after tapping on a notification, or just having the app open when a transaction goes through. It’s now my number 2 most hated part of Monzo after the whole pre-authorisation affecting the balance thing (which, in the grand scheme of things, is pretty good for Monzo having a sound effect as the second most hated thing).