Add Support for ARN as DynamoDB Standard Type

### Describe the feature

Update DynamoDB client to natively support a new datatype: `com.amazonaws.arn.Arn`

### Use Case

We store many ARNs in our DynamoDB instance related to SQS topics, StepFunctions State Machines, etc. - would be nice for to have native support for ARNs in DynamoDB mapper.

### Proposed Solution

Add ARN support to list of standard supported types.

https://github.com/aws/aws-sdk-java/blob/master/aws-java-sdk-dynamodb/src/main/java/com/amazonaws/services/dynamodbv2/datamodeling/StandardTypeConverters.java#L83

### Other Information

* https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/DynamoDBMapper.DataTypes.html
* https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/HowItWorks.NamingRulesDataTypes.html
* https://sdk.amazonaws.com/java/api/latest/software/amazon/awssdk/arns/Arn.html

### Acknowledgements

- [X] I may be able to implement this feature request
- [ ] This feature might incur a breaking change

### AWS Java SDK version used

2

### JDK version used

JDK 11

### Operating System and version

Linux