(aws-sso): Context Provider for SSO Instances.

### Describe the feature

A context provider that will return the id of the identity source for SSO.

### Use Case

An Identity Center Group, requires the Id of the identity Store to create a Group.

```
const group = new aws_identitystore.CfnGroup(this, 'Resource', {
identityStoreId: props.identityStoreId,
description: props.description,
displayName: props.name,
});
```

Currently this can be provided, manually by providing a value in cdk.json, or a slightly anti-pattern custom resource lookup.

Groups are at the heart of creating policy for Verified Permissions and Verified Access.

### Proposed Solution

Implement a IdentityCenterStore Id Context Procider Plugin.. The can follow the pattern of other providers, such as [hosted-zones](https://github.com/aws/aws-cdk/blob/eea223b52f4445e6084b1fa1fa15a3a78f83fa18/packages/aws-cdk/lib/context-providers/hosted-zones.ts)

### Other Information

- A custom resource can be used to get the value, but this has the possiblity of non determinism if the value changed, so is anti-pattern.

- The value can be provided manually in cdk.context.

### Acknowledgements

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

### CDK version used

2.85.0

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

any

Start by reading packages/aws-cdk/lib/context-providers/hosted-zones.ts to understand the existing context-provider pattern, then trace how a provider for an Identity Center identity store would be registered and queried. Done means the provider returns the identity store ID needed by an Identity Center Group without requiring a manual cdk.context value or custom resource.

Written by the indexing model from the issue text.