Determines which shard in the stream the data record is assigned to. Partition keys are Unicode strings with a maximum length limit of 256
            bytes. Amazon Kinesis uses the partition key as input to a hash function that maps the partition key and associated data to a specific
            shard. Specifically, an MD5 hash function is used to map partition keys to 128-bit integer values and to map associated data records to
            shards. As a result of this hashing mechanism, all data records with the same partition key will map to the same shard within the stream.
             
            
Constraints:
 Declaration Syntax
 Declaration Syntax| C# | 
public string PartitionKey { get; set; }