batch: Support multi-container job definitions

### Describe the feature

https://docs.aws.amazon.com/batch/latest/userguide/multi-container-jobs.html This indicates that both the AWS CLI/API and Cloudformation support this feature.

The README for the Batch CDK module also seems to indicate that this is possible. If it only means to talk about multi-node job definitions, that isn't clear.

However, I've also noticed the modified CloudFormation properties aren't documented, so I've also raised https://github.com/aws-cloudformation/cloudformation-coverage-roadmap/issues/1941, which I assume would be a blocker.

### Use Case

I want to run the Datadog Agent in a sidecar container so we can instrument our Batch Jobs with APM and ship logs to Datadog from our Batch jobs via the agent rather than through a subscription on the Log Group

### Proposed Solution

_No response_

### Other Information

_No response_

### Acknowledgements

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

### CDK version used

any

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

N/A

Read the Batch CDK module README and the AWS Batch multi-container jobs documentation first, then compare the documented multi-node behavior with CloudFormation coverage-roadmap issue #1941. Confirm which CloudFormation properties are available before identifying the relevant CDK entry points and tests. Done means multi-container job definitions are supported and the README clearly documents their scope.

Written by the indexing model from the issue text.