Store WAC permissions in their own named graph

In the current implementation, WAC permissions are all saved in a custom SemApps-specific named graph. While it would be technically possible to keep this with NextGraph, the standard-compliant way to do this would be to store WAC permissions as regular resources, in their own document (and thus their own named graph)

This will require quite a lot of refactoring. It should probably be done closely with https://github.com/assemblee-virtuelle/semapps/issues/1189

- Automatically create a WAC permission every time a new LDP resource or container is created.
- Put it on the same container as the resource ?
- Automatically link it to the LDP resource with the `acl:accessControl` predicate
- This is the one used by StartinBlox
- This predicate is described like this in the [ACL ontology](https://www.w3.org/ns/auth/acl#): _"The Access Control file for this information resource. This may of course be a virtual resource implemented by the access control system."_
- When a LDP resource or container is deleted, also delete the WAC permissions
- If ActivityPub Tombstones are activated, the WAC permissions should be erased and we should only keep a public read permission.
- Migration tool
- Go through all LDP resources and containers, create a Document with a WAC permissions. Look at the existing permissions of the resource or container. Add a `acl:accessControl` link from the resource.

Review the current WAC permission and named-graph implementation alongside issue #1189; the payload does not name specific files or tests. Define the resource lifecycle, acl:accessControl link, deletion and tombstone behavior, and migration requirements before implementing. Done means permissions are separate resources in their own documents and existing resources are migrated.

Written by the indexing model from the issue text.