add an initialization script to aws-cdk-lib.aws_efs module

### Describe the feature

allow a set of commands to be executed when the elastic file system is created.

### Use Case

Allowing to create a set of directories when the elastic file system is created.
Currently every lambda invocation needs to check if the working directories exists and create them if it's not the case.

### Proposed Solution

adding an initialisation data that take a set of commands similar to `ec2Instance.userData.addCommands();`

### Other Information

_No response_

### Acknowledgements

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

### CDK version used

1.152.0

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

macos 12

The requested entry point is the aws-cdk-lib.aws_efs module; inspect its file-system creation API and related tests to find where initialization data could fit. First verify the lifecycle constraints for running commands when an Elastic File System is created. Done should provide a documented and tested way to supply commands for creating initial working directories.

Written by the indexing model from the issue text.