Limit room visibility by space power level

### Your use case

#### What would you like to do?
It would be quite useful in large communities to have a system for restricting if a room is visible depending on if the user is a certain power level in the space it's public in.

#### Why would you like to do it?
This would provide a way for organisations or even large communities who frequently accept new members to have a trust-like system that would be used to prevent new or lower ranking members from viewing certain rooms until they reach a certain level, while leaving more experienced and trusted users to access these rooms as a normal room public to a space.

#### How would you like to achieve it?
When a room is added to a space it could also have an input box below that would allow for selection of a minimum power level required to be shown, or alternatively in the space "roles and permissions" section in settings there could be a list of all rooms and their respective minimum required level.

### Have you considered any alternatives?

For now keeping some rooms private and manually inviting members to them suffices, although that solution is not scalable as a space grows larger.

### Additional context

Thank you for taking the time to read these suggestions. I really appreciate it.

The issue names no files, tests, or entry points. Start by clarifying where space power levels, room visibility, and the space roles and permissions settings are handled. Done means a room can have a minimum required power level, users below it cannot see the room, and the existing private-room invitation alternative remains supported.

Written by the indexing model from the issue text.