Add chess app server-side Blazor sample

[mjrousos]

This adds a server-side Blazor sample based on a larger learning project I worked on recently. The sample presents users with chess tactics puzzles and demonstrates:

1. Blazor components for providing non-trivial interactions (such as moving pieces on a chess board).
2. Using OwningComponentBase for managing DI scopes (especially with EF Core).
3. Integrating with Material Design Components for Web for styling.
4. Integrating with Azure AD B2C for auth.

The learning project this was extracted from is deployed at https://chesstrainerapp.azurewebsites.net/.