Authentication without Cognito Users, federated only

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

_No response_

### Is this related to another service?

_No response_

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

It should be possible to configure authentication so that one or more social providers can be used without setting up options for native cognito users.

It does not always make sense for an application to want to manage its own user accounts

### Describe the solution you'd like

A new option when adding auth

Do you want to use the default authentication and security configuration? (Use arrow keys)
> Default configuration
Default configuration with Social Provider (Federation)
**Social Provider without cognito default**
Manual configuration
I want to learn more.

### Describe alternatives you've considered

Option 1 Using Manual configuration option but this insists on setting up cognito users

Option 2
Configuring cognito users but only displaying custom dedicated social signin buttons and not using the authenticator UI at all.
Unfortunately that is not full proof as in some cases the UI falls back to rendering the authenticator view including cognito username and password

### 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 tracing the Amplify CLI auth-add flow and its Cognito federation configuration. Determine how the proposed social-provider-only option should be represented and validated, then identify tests covering auth configuration; done means a user can configure federated providers without native Cognito users and the resulting setup avoids username/password UI.

Written by the indexing model from the issue text.