Gets and sets the property CallerReference. A unique number that ensures the request
            can't be replayed.    If the CallerReference is new (no matter the content of the
            DistributionConfig object), a new distribution is created.    If the CallerReference
            is a value you already sent in a previous request to create a distribution, and the
            content of the DistributionConfig is identical to the original request (ignoring white
            space),    the response includes the same information returned to the original request.
               If the CallerReference is a value you already sent in a previous request to create
            a distribution but the content of the DistributionConfig is different from the original
            request,    CloudFront returns a DistributionAlreadyExists error.
            
 Declaration Syntax
 Declaration Syntax| C# | 
public string CallerReference { get; set; }