✨(backend) add soft delete to documents and refactor db queryset

Now that we have introduced a document tree structure, it is not
possible to allow deleting documents anymore as it impacts the whole
subtree below the deleted document and the consequences are too big.

We introduce soft delete in order to give a second thought to the
document's owner (who is the only one to be allowed to delete a
document). After a document is soft deleted, the owner can still
see it in the trashbin (/api/v1.0/documents/trashbin).
After a grace period (30 days be default) the document disappears
from the trashbin and can't be restored anymore. Note that even
then it is still kept in database. Cleaning the database to erase
deleted documents after the grace period can be done as a maintenance
script.

src/backend/core/api/utils.py

@@ -11,6 +11,29 @@ import botocore
 from rest_framework.throttling import BaseThrottle
 
 
+def filter_root_paths(paths, skip_sorting=False):
+    """
+    Filters root paths from a list of paths representing a tree structure.
+    A root path is defined as a path that is not a prefix of any other path.
+
+    Args:
+        paths (list of str): The list of paths.
+
+    Returns:
+        list of str: The filtered list of root paths.
+    """
+    if not skip_sorting:
+        paths.sort()
+
+    root_paths = []
+    for path in paths:
+        # If the current path is not a prefix of the last added root path, add it
+        if not root_paths or not path.startswith(root_paths[-1]):
+            root_paths.append(path)
+
+    return root_paths
+
+
 def generate_s3_authorization_headers(key):
     """
     Generate authorization headers for an s3 object.