[adapters] Use an adapter for serializing entities to a bare python structure
which may be used for e.g. JSON export or other and allow to have different
serializations for each entity types.
Closes #6378035
change_attribute_type('CWCache', 'timestamp', 'TZDatetime')
change_attribute_type('CWUser', 'last_login_time', 'TZDatetime')
change_attribute_type('CWSource', 'latest_retrieval', 'TZDatetime')
drop_attribute('CWSource', 'synchronizing')
add_attribute('CWSource', 'in_synchronization')