(lambda_event_sources): DocumentDB eventSource not supported

### Describe the feature

A DocumentDB event source mapping is supported in lambda event source mappings.

But L2 Construct does not exist.

See [Lambda event source mappings](https://docs.aws.amazon.com/lambda/latest/dg/invocation-eventsourcemapping.html)

### Use Case

To use DocumentDB as a event source.

### Proposed Solution

Add `DocumentDBSource` class to the `aws_lambda_event_sources`.

### Other Information

_No response_

### Acknowledgements

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

### CDK version used

2.141.0

### Environment details (OS name and version, etc.)

MacOS

Start in the aws_lambda_event_sources module and compare its existing event source classes with the Lambda event source mappings documentation, focusing on the proposed DocumentDBSource class. Done means the module exposes a DocumentDB event source mapping for use with Lambda, with coverage consistent with the surrounding event source implementations.

Written by the indexing model from the issue text.