REST API supports loading and saving dynamic attributes.
In order to load dynamic attributes of an entity instance, add the dynamicAttributes=true parameter
to the find or query request:
app-portal/api/find.xml?e=sample$Car-9f789ba9-ca15-4758-a8b8-77e434f1d438&s=9f789ba9-ca15-4758-a8b8-77e434f1d438&dynamicAttributes=true
Dynamic attributes are represented in JSON and XML documents in the same way as regular attributes, except
for the preceding + symbol.
REST API also saves dynamic attributes passed to commit.
