When multiple Doctrine Documents are stored in the same namespace (using 
InheritanceType SINGLE_COLLECTION), the encrypted fields maps generated from the metadata of each document classes should be merged into a single entry for the collection.
 
This need to be done in SchemaManager when the collection is created, and in the dump-encrypted-fields-map command.
 
Question: what should be the behavior when the same field path has different configurations in different document classes using the same namespace?