Add support for batch in `Message<List<Message<?>>>` structure

[artembilan]

Right now batch support is present as a message of list of payloads and individual headers are stored as an item of list in some specific header.
The structure as Message<List<Message<?>>> makes it easier to navigate individual items in the batch with their specific header and so on.

The example is a result of Kinesis Binder on the consumer side:

[olegz]

From the s-c-function perspective this should be fairly easy to implement since it is really about message conversion and expectation of the converter.

[github-actions]

This issue has been stale for over 60 days