[JS] DynamoDB UpdateItem return old values on ConditionalCheckFailedException

[Docs](https://docs.aws.amazon.com/appsync/latest/devguide/js-resolver-reference-dynamodb.html#js-aws-appsync-resolver-reference-dynamodb-condition-expressions) state that one should be able to see that data by default on `ctx.error.data`, but this doesn't seem to be the case.

```json
{
"arguments": {
"recordInput": {
"id": "1",
"sk": "1"
}
},
"prev": {
"result": {}
},
"stash": {},
"error": {
"message": "The conditional request failed (Service: DynamoDb, Status Code: 400, Request ID: 3S...)",
"type": "DynamoDB:ConditionalCheckFailedException"
},
"outErrors": []
}
```
There is also no `returnValuesOnConditionCheckFailure` attribute for the `UpdateItem` operation allowed.

Actual response (where docs state we should also be able to see the old/current record values):
```json
{
"data": {
"extendTtl": null
},
"errors": [
{
"path": [
"extendTtl"
],
"data": null,
"errorType": null,
"errorInfo": null,
"locations": [
{
"line": 2,
"column": 3,
"sourceName": null
}
],
"message": "The conditional request failed (Service: DynamoDb, Status Code: 400, Request ID: 3S...)"
}
]
}
```

With `TransactWriteItems`, where for some reason you can actually use `returnValuesOnConditionCheckFailure` for an `UpdateItem` operation, it seems to work as expected and the value is reachable in the ctx:
```json
{
"arguments": {
"recordInput": {
"id": "1",
"sk": "1"
}
},
"result": {
"cancellationReasons": [
{
"type": "ConditionalCheckFailed",
"message": "The conditional request failed",
"item": {
"test": {
"test1": true
},
"sk": "1",
"testField": "1-1",
"id": "1",
"ttl": 1705338604
}
}
]
},
"prev": {
"result": {}
},
"stash": {},
"error": {
"message": "Transaction cancelled, please refer cancellation reasons for specific reasons [ConditionalCheckFailed] (Service: DynamoDb, Status Code: 400, Request ID: OTL...)",
"type": "DynamoDB:TransactionCanceledException"
},
"outErrors": []
}
```
But using `TransactWriteItems` isn't really an option, as it doesn't return all values of the updated record...

Start with the linked AppSync JavaScript resolver DynamoDB condition-expression documentation and compare the documented UpdateItem behavior with the reported ctx.error.data output. Check the allowed UpdateItem attributes against TransactWriteItems, and consider the issue resolved only when the behavior is corrected or the documentation clearly reflects the supported response.

Written by the indexing model from the issue text.