Add ASP.NET Core Identity Endpoints scaffolder

The [ASP.NET Core Identity endpoints](https://learn.microsoft.com/aspnet/core/security/authentication/identity-api-authorization) provide programmatic access to the identity system. The prebuilt endpoints included in ASP.NET Core Identity don't allow for much customization. To enable customization, we [propose](https://github.com/dotnet/aspnetcore/issues/53343) to add a scaffolder to include the implementation of the ASP.NET Core Identity endpoints in the user's project similar to how we support scaffolding the identity UI code. This would allow the user to customize the endpoints as they see fit.