Spaces with no manager

## Describe the bug

An space should always have at least one `manager`. There is a way to force an space to have no managers.

## Steps to reproduce

1. In a space, set two managers
2. Set expiration date for both
3. Turn one of the managers into another role (`editor` or `viewer`), so, there is only one manager, who keeps the expiration date set in step 2.
4. Wait till the expiration date is due

## Expected behavior

Several options:

- `manager` should stay as `manager`, ignoring the expiration date
- any other user is assigned as new `manager` as the existing one is removed from the space
- expiration dates do not apply to the `manager` role if there are no other `manager` in the space

Spaces always have at least one manager.

## Actual behavior

no managers in the space, because the only one was out because the expiration date was due

## Setup