♻️(backend) stop requiring owner for non-root documents

If root documents are guaranteed to have a owner, non-root documents
will automatically have them as owner by inheritance. We should not
require non-root documents to have their own direct owner because
this will make it difficult to manage access rights when we move
documents around or when we want to remove access rights for someone
on a document subtree... There should be as few overrides as possible.

CHANGELOG.md

@@ -25,6 +25,7 @@ and this project adheres to
 
 ### Changed
 
+- ♻️(backend) stop requiring owner for non-root documents #846
 - ♻️(backend) simplify roles by ranking them and return only the max role #846
 - 📌(yjs) stop pinning node to minor version on yjs docker image #1005
 - 🧑‍💻(docker) add .next to .dockerignore #1055