Add multi-tenant guidance for .NET

[amerjusupovic]

Inspired by this comment.

[Copilot]

Pull Request Overview

Adds guidance for configuring multi-tenant applications in .NET and corrects minor typos in the WebDemo example.

• Fixed spelling of "overridden" in cache expiration comments for Azure App Configuration and feature flags.
• Introduced a new README with step-by-step instructions for setting up per-tenant settings using the options pattern.

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
examples/DotNetCore/WebDemoNet6/WebDemoNet6/Program.cs	Corrected spelling in comment “overridden”
examples/DotNetCore/MultiTenantApplicationSetup/README.md	Added multi-tenant application setup instructions for .NET

Comments suppressed due to low confidence (1)

examples/DotNetCore/MultiTenantApplicationSetup/README.md:73

• Before registering ConfigureTenantSettings, add services.AddHttpContextAccessor() to ensure IHttpContextAccessor is available in the DI container.

services.AddScoped<IConfigureOptions<TenantSettings>, ConfigureTenantSettings>();