Follow up to Create materiallist for collaboration

Follow up to #2452

- [ ] Set the materiallist to the name of the collaborator when the campcollaboration is deleted. https://github.com/ecamp/ecamp3/pull/2452#discussion_r832152215 and follow up
https://github.com/ecamp/ecamp3/pull/2452#discussion_r832505798
@BacLuc : If 2 people have the same name, they cannot change the name of the campcollaboration that they can be distinguished.
Alternative: return null and translate the fallback in the frontend.
- [ ] Eventually remove the flush in CampCollaborationPersister https://github.com/ecamp/ecamp3/pull/2452#discussion_r832504118
(To be discussed)
- [x] When cloning a camp (Either from a prototype or from an existing camp), (https://github.com/ecamp/ecamp3/pull/2452#discussion_r837314111)
1. should the reference Materiallist->campCollaboration be preserved,
2. null written into the materiallist name
3. the name of the collaborator be copied?
4. New: the material list not be copied? (this is implemented now)