[IAM] Allow restricting identities and roles

### TL;DR

Have a config file, read from main that limits the member identities and roles/permissions that are allowed to be given

### Detailed design

_No response_

### Alternatives considered

_No response_

### Additional information

_No response_

Look for the main configuration file and IAM-related code to understand how identities and roles are currently managed. The issue mentions adding a config file to restrict allowed member identities and roles/permissions. Start by examining the existing IAM structure and configuration parsing. Determine where validation logic should be added and what 'done' looks like: a configurable restriction system that limits what can be granted.

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