Cognito: User pool managed login branding designer support

### Describe the feature

AWS recently introduced user pool managed login, providing API support for this feature. This request is to add CDK support for the feature.

Reference: [AWS Cognito User Pools Managed Login Branding Designer](https://docs.aws.amazon.com/cognito/latest/developerguide/managed-login-brandingdesigner.html)

### Use Case

1. Infrastructure as Code (IaC): It allows developers to programmatically define and deploy managed login configurations within their existing CDK stacks.
2. Consistency: Ensures the managed login setup is version-controlled and replicable across environments, reducing configuration drift.
3. Automation: Simplifies the deployment process by integrating the managed login feature into automated CI/CD pipelines.
4. Ease of Use: Developers can leverage familiar programming languages to configure managed login instead of manually setting it up in the AWS Console or through separate API calls.

### Proposed Solution

_No response_

### Other Information

_No response_

### Acknowledgements

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

### CDK version used

2.172.0

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

NA

Start with the AWS Cognito managed login branding designer reference and the existing CDK Cognito user-pool entry points. Determine which managed-login branding configuration the CDK should expose and how it maps to the AWS API. Done means the feature is defined clearly enough to configure and deploy through a CDK stack, with appropriate validation and tests.

Written by the indexing model from the issue text.