Add: (ement-room-hide-redacted-message-content) New option

@phil-s What do you think about this as a new default? I had considered implementing a button to toggle the visibility of redacted messages, but I'm not sure the complexity would be worth it. This seems like a good and simple default behavior to protect users from seeing unpleasant content that has since been redacted, while still allowing it to be overridden if necessary.