Add a toString method for S3EventNotificationRecord class

[ashunimbz]

Currently while logging S3Event instance , toString just logs hash code .

S3Event toString() method in turn calls S3EventNotificationRecord toString() method which is not present . Hence it defaults to plain objects toString() method which in turn just logs hash code rendering toString() method of S3Event class useless .

aws-lambda-java-libs/aws-lambda-java-events/src/main/java/com/amazonaws/services/lambda/runtime/events/S3Event.java

Line 25 in 4fe08f4

public class S3Event extends S3EventNotification implements Serializable, Cloneable {

[msailes]

I've created a pull request #302

The output is quite verbose, maybe there are improvements which could be main.

{
   [
      S3EventNotificationRecord{
         "awsRegion=""eu-central-1",
         "eventName=""ObjectCreated:Put",
         "eventSource=""aws:s3",
         "eventTime=1970-01-01T00":"00":00.000Z,
         "eventVersion=""2.0",
         "requestParameters=RequestParametersEntity"{
            "sourceIPAddress=""127.0.0.1"
         },
         "responseElements=ResponseElementsEntity"{
            xAmzId2="EXAMPLE123/5678abcdefghijklambdaisawesome/mnopqrstuvwxyzABCDEFGH",
            "xAmzRequestId=""EXAMPLE123456789"
         },
         s3=S3Entity{
            "configurationId=""testConfigRule",
            bucket=S3BucketEntity{
               "name=""example-bucket",
               "ownerIdentity=UserIdentityEntity"{
                  "principalId=""EXAMPLE"
               },
               "arn=""arn:aws:s3:::example-bucket"
            },
            object=S3ObjectEntity{
               "key=""test/key",
               size=1024,
               "eTag=""0123456789abcdef0123456789abcdef",
               "versionId=""",
               "sequencer=""0A1B2C3D4E5F678901"
            },
            s3SchemaVersion="1.0"
         },
         "userIdentity=UserIdentityEntity"{
            "principalId=""EXAMPLE"
         }
      }
   ]
}

[msailes]

This will be fixed in v4