Use this annotation to specify that a field is a data key, optionally providing the data key name
to use.
If the data key name is not specified, the default is the Java field's name. For example:
public class A {
// uses data key name of "dataKeyNameMatchesFieldName"
@Key
public String dataKeyNameMatchesFieldName;
// uses data key name of "some_other_name"
@Key("some_other_name")
private String dataKeyNameIsOverridden;
// not a data key
private String notADataKey;
}