EC2 MachineImage: support for cross account ssm parameter

### Describe the feature

`MachineImage.from_ssm_parameter(parameter_name=....)` doesn't support cross-account parameters. You cannot provide an ARN. I believe the module should support fetching of AMI ID from shared SSM parameters.

### Use Case

It's very likely to publish SSM parameters with AMI ID from a centralised account, when creating new EC2 instances `MachineImage.from_ssm_parameter(parameter_name=....)` should support the lookup of them.

### Proposed Solution

_No response_

### Other Information

_No response_

### Acknowledgements

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

### CDK version used

2.159.1 (build c66f4e3)

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

Linux

Start by tracing MachineImage.from_ssm_parameter(parameter_name=...) in the AWS CDK code and inspect how the current SSM parameter lookup handles the parameter name. Determine how an ARN for a shared cross-account parameter should be accepted and verify that the AMI ID can be fetched for the EC2 image lookup.

Written by the indexing model from the issue text.