(aws-servicecatalog): ProductStack Env

### Describe the feature

We want to be able to specify the env for the ProductStack, ie. account and/or region.

### Use Case

In CDK Pipeline currently the ProductStack takes its env from the stage.
In our usecase we need the Product to either be account agnostic or use an account different from the stage.

However, for cross-region deployments an account needs to be specified on the stage.
This results in breaking behaviour with our account requirement from above

### Proposed Solution

Expose an `env` property similar to regular stacks

### Other Information

_No response_

### Acknowledgements

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

### CDK version used

2.129.0

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

Mac

Start by locating the ProductStack implementation and the code that currently derives its env from the stage. Trace how account and region are propagated during CDK Pipeline deployments, including cross-region cases. Done means ProductStack exposes an env property like regular stacks and supports account-agnostic or explicitly targeted account and region behavior without breaking stage-based use.

Written by the indexing model from the issue text.