app-staging-synthesizer: cross-account support

### Describe the feature

I do not see an option to add a trust relationship to the roles created by the new app-staging-synthsizer.
But they are required to provide a similar experience as the current default bootstrap for cross-account deployments.

### Use Case

We have three accounts: dev, prod and one for the pipeline

### Proposed Solution

I think adding an array of trusted accounts to https://github.com/aws/aws-cdk/blob/a35fcc59b227cc6151c50ebd04a7b9f9fb3bc189/packages/%40aws-cdk/app-staging-synthesizer-alpha/lib/default-staging-stack.ts#L45 might work. `IPrincipal[]` could be used.

Then adding a `CompositePrincipal` with the account and the added trusted accounts should be enough.

### 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

-

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

-

Start with packages/@aws-cdk/app-staging-synthesizer-alpha/lib/default-staging-stack.ts at the referenced role definition, then compare it with the current default bootstrap’s cross-account behavior. Determine how trusted accounts should be exposed and represented in the generated roles; done means deployments across the dev, prod, and pipeline accounts receive the required trust relationship.

Written by the indexing model from the issue text.