Update the copy and visuals for the Room Settings: Notifications page

This is part of the #24291 Epic and shouldn't be shipped independently (there needs to be a defined migration path).
Settings are changing to be simpler and easier to grok for all users

We need to:
- Update the Room Settings notifications modal to reflect the new choices available to users based on the changes to Settings.
- Update the custom sound section for power users so that it's in-keeping with our design system but still accessible for those who use it (pending design)
- As the sound settings per room as complicated, handled in global settings and you can put a room on mute/loud, we will be removing the "turn sound off for this room" option/ or disabling it when not available (pending design)
- Update the content and notification settings in the modal to match the designs in [figma here](https://www.figma.com/file/M15i7l4PSPY1B5M7Zhu80H/Notifications?type=design&node-id=9293-141929&t=c2GVrjdTV8mcGfcp-0)

```[tasklist]
### Tasks
- [ ] https://github.com/vector-im/element-web/issues/24524
- [ ] https://github.com/vector-im/element-web/issues/24525
- [ ] https://github.com/vector-im/element-web/issues/24526
```