Ban a user from a space who currently isn't in that space

### Your use case

#### What would you like to do?

Ban a user from a space, even though they're not currently in that space.

#### Why would you like to do it?

Perhaps a misbehaving user leaves of their own accord, but a moderator would like to prevent them from returning, or a moderator would like to prevent a user in one community from coming to other communities.

#### How would you like to achieve it?

Unsure. Apparently for rooms this is typically done using the /ban command, which isn't accessible in spaces.

### Have you considered any alternatives?

No

### Additional context

This conversation in the spaces feedback room brought this up as a needed feature: https://matrix.to/#/!LPqOcoJQuGkweiTedq:riot.ovh/$g0jMZQia4AbcrJ8uFPPCxYY4C9wjVlMRvccVPp0EPRA?via=townsendandsmith.ml&via=matrix.org&via=envs.net