Add a note about ASP.NET Core Identity migrations

[AndriySvyryd]

No description provided.

[Copilot]

Pull Request Overview

This PR adds documentation about handling ASP.NET Core Identity configuration changes that can trigger the "pending model changes" warning in Entity Framework Core 9.0. The addition provides guidance for scenarios where Identity options affecting the model cause migration issues.

• Expands the list of scenarios that can cause the "pending model changes" warning
• Provides specific mitigation guidance for ASP.NET Core Identity configuration changes
• Includes code examples showing both the problematic configuration and the recommended solution using IDesignTimeDbContextFactory