Adding entry_ids to assocs built with cast_assoc

[Danwhy]

If we apply the cast_assoc function to a changeset, the association is added to the changes, and will be inserted into the database if it doesn't exist.

This can cause a problem for us, as the association will be inserted without an entry id.

To fix this, when adding the entry_id on the insert function, we should iterate through the changes, checking if there are any nested changesets, and add entry_ids to those too.