neptune: construct should allow restoration from a snapshot

### Describe the feature

The snapshotIdentifier would work very similar to the underlying RDS feature (https://docs.aws.amazon.com/cdk/api/v2/docs/aws-cdk-lib.aws_rds.CfnDBCluster.html). This would take in an ARN or another identifier and restore the Neptune database from the snapshot that matches the identifier.

This change would work as a construct built here https://docs.aws.amazon.com/cdk/api/v2/docs/@aws-cdk_aws-neptune-alpha.DatabaseCluster.html

### Use Case

Users require the ability to save snapshots of their Neptune database and restore from that snapshot in the case of a critical failure. This field would allow restoration from a snapshot while deploying applications that utilize cloud formation.

### Proposed Solution

Inclusion of the snapshotIdenfier property built into RDS - https://docs.aws.amazon.com/cdk/api/v2/docs/aws-cdk-lib.aws_rds.CfnDBCluster.html

### 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

2.73.0

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

Mac OSX, Linux

Start at the aws-neptune-alpha.DatabaseCluster construct and compare its supported configuration with the AWS RDS CfnDBCluster snapshotIdentifier documentation linked in the issue. Trace how DatabaseCluster properties are represented in the synthesized CloudFormation template, then verify that a snapshot identifier produces the expected Neptune restoration configuration.

Written by the indexing model from the issue text.