AttributeType 'SS' not allowed

[tracey-ruark]

Describe the issue
We've got an existing dynalite implementation up and running, using jest-dynalite-config.js to configure our tables. We're attempting to add attributes to an existing table to store an array of string values and we ran into the error: ValidationException: 2 validation errors detected: Value 'SS' at 'attributeDefinitions.2.member.attributeType' failed to satisfy constraint: Member must satisfy enum value set: [B, N, S]; Value 'SS' at 'attributeDefinitions.3.member.attributeType' failed to satisfy constraint: Member must satisfy enum value set: [B, N, S]

Steps to reproduce
Here is the configuration block of the existing table inside of our jest-dynalite-config.js file prior to the changes:

{
  TableName: `service-store`,
  KeySchema: [
    {
      AttributeName: 'serviceName',
      KeyType: 'HASH'
    }
  ],
  AttributeDefinitions: [
    {
      AttributeName: 'serviceName',
      AttributeType: 'S'
    }
  ],
  ProvisionedThroughput: {
    ReadCapacityUnits: 1,
    WriteCapacityUnits: 1
  }
}

Modified as follows to add two new attributes with the 'SS' AttributeType:

{
  TableName: `service-store`,
  KeySchema: [
    {
      AttributeName: 'serviceName',
      KeyType: 'HASH'
    }
  ],
  AttributeDefinitions: [
    {
      AttributeName: 'serviceName',
      AttributeType: 'S'
    },
    {
      AttributeName: 'testTypes',
      AttributeType: 'SS'
    },
    {
      AttributeName: 'testEnvs',
      AttributeType: 'SS'
    }
  ],
  ProvisionedThroughput: {
    ReadCapacityUnits: 1,
    WriteCapacityUnits: 1
  }
}

Expected behavior
DynamoDB documentation indicates that the 'SS' type is a valid attribute type for representing a String Set, as long as it is not used for Hash or Range Keys. Since this isn't being used as a Hash or Range key we would expect it to work the same in Dynalite as it would in DynamoDB.