Add option to show all rooms in nested spaces

### Your use case

#### What would you like to do?
Just as in classic Element (and Web), I want to be able to see all rooms in a Space, even if they are nested somewhere in a more complex space hierachy

#### Why would you like to do it?
Some Spaces are just used to control access to different rooms, whereas they belong to the same bigger domain.

Hiding the rooms lower in the hierarchy means, I have to click multiple times, wait for the 2-3s load delay in loading a space. And this on every app start, as the current space isn't remembered throughout sessions

#### How would you like to achieve it?
Give me an option to show em all please! :)

### Have you considered any alternatives?

Using element classic I guess

### Additional context

_No response_

### Are you willing to provide a PR?

No