Initialise AMI-based deployment with a Core database dump

- Should be useful when migrating to AMI-based deployments from different deployment strategies.
- AMI should be the recommended deployment on AWS.
- Add an optional CloudFormation parameter to support AMI-based migrations by allowing the administrator to provide a URL to a Core database dump stored in an S3 bucket.
- When the parameter is set, the deployment must automatically download and restore the dump into the newly created database during stack creation.
- When it is not set, the stack must behave exactly as it does today (fresh database).
- Add proper error handling and fail the deployment clearly if the dump cannot be downloaded or applied.