DynamoDB Enhanced Client: batch writes

### Describe the feature

Requested feature: `batchPutItem(Collection)` and `batchUpdateItem(Collection)` methods on `DynamoDbTable`.

### Use Case

The low-level client supports batch transactional writes, and the Enhanced client works by mapping POJOs onto low-level operations. I would like to write a series of records transactionally from POJOs, but the Enhanced client only supports single-record operations. Instead, I want to prepare the records to be saved and save them as a batch.

### Proposed Solution

`PutItemOperation` (with the other `TableOperation`s) generates a `PutItemRequest`, and the low-level client already supports the `batchWriteItem` operation that takes multiple `PutItemRequest`s and batches them. All of the existing logic for the Enhanced client could remain in place with a scatter-gather implementation that collects the generated requests and executes them via `batchWriteItem`.

### Other Information

_No response_

### Acknowledgements

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

### AWS Java SDK version used

2.17.260

### JDK version used

OpenJDK 64-Bit Server VM AdoptOpenJDK-11.0.11+9 (build 11.0.11+9, mixed mode)

### Operating System and version

Gentoo Linux