Annotation for marking a hash key or range key property in a class to
auto-generate this key. Only String typed keys can be auto generated, and are
given a random UUID. The annotation can be applied to either the getter
method or the class field for the auto-generated key property. If the
annotation is applied directly to the class field, the corresponding getter
and setter must be declared in the same class. This annotation can be applied
to both primary and index keys.