Protect the space metafiles.

## Describe the bug
Protect the hidden space metafiles `.space` and `.space/readme.md` from deleting or moving.
Based on rejected issue [#8719](https://github.com/owncloud/ocis/issues/8719) we want to merge the already implemented useful part.

## Expected behavior
A clear and concise description of what you expected to happen.

## Actual behavior
A clear and concise description of what happened.

## Setup
Please describe how you started the server and provide a list of relevant environment variables or configuration files.

```console
OCIS_XXX=somevalue
OCIS_YYY=somevalue
PROXY_XXX=somevalue
```

## Additional context
Add any other context about the problem here.

Start by reviewing rejected issue #8719 and locating the already implemented useful portion referenced there. Trace the server's delete and move handling for `.space` and `.space/readme.md`; done means both metafiles are protected from those operations and the relevant behavior is covered by tests.

Written by the indexing model from the issue text.