Allow viewing rooms in a space before joining it

#### Is your suggestion related to a problem? Please describe.

We are trying out Spaces Beta and would like to make a public space viewable by guests. However, the room ACL does not matter because one has to be logged in to enable the Spaces Beta. In the end we can only share the links to the individual rooms inside the space in order to have them be viewable by guests, which makes it more difficult to try out Spaces properly, because people are then more likely to just join the individual rooms and not the wider Spaces room.

#### Describe the solution you'd like.

Allow a guest user to enroll in the Spaces Beta, or perhaps even automatically enable it when they try to access a Spaces room from a URL.

#### Describe alternatives you've considered.

An alternative might be to provide a simpler room listing interface for guests to access the rooms inside the Spaces room.

#### Additional context

Here is a Spaces room for example: https://matrix.to/#/#krita-users:kde.org