Using parameter in function custom polices

### Is this feature request related to a new or existing Amplify category?

_No response_

### Is this related to another service?

lambda

### Describe the feature you'd like to request

I dont find any docs regarding using cloud formation parameter in custom-polices.json file?

### Describe the solution you'd like

Adding support or document

### Describe alternatives you've considered

N/A

### Additional context

_No response_

### Is this something that you'd be interested in working on?

- [ ] 👋 I may be able to implement this feature request

### Would this feature include a breaking change?

- [ ] ⚠️ This feature might incur a breaking change

Start by locating how the Amplify CLI reads and validates custom-policies.json, then trace whether CloudFormation parameters are handled in that path. Review the existing Lambda and custom-policy documentation if present. Done requires a decided scope—documenting supported parameter usage or implementing support—with coverage for the chosen behavior.

Written by the indexing model from the issue text.