Add certificate trust customization article for Aspire 13

[Copilot]

Summary

This PR adds comprehensive documentation for the new certificate trust customization features introduced in Aspire 13, addressing issue #5307.

Changes

• Created docs/app-host/certificate-trust.md: A comprehensive article documenting how to customize trusted certificates for Executable and Container resources
• Updated docs/toc.yml: Added the new article to the AppHost section, positioned after "AppHost configuration"

Article Coverage

The new article provides detailed documentation on:

Core Features

• Certificate Authority Collections: How to create and use custom certificate bundles using AddCertificateAuthorityCollection, WithCertificates, and WithCertificateAuthorityCollection APIs
• Development Certificate Trust: Automatic trust for ASP.NET Core Development Certificate (enabled by default) and the WithDeveloperCertificateTrust API for per-resource control
• Certificate Trust Scopes: Four modes (Append, Override, System, None) using the WithCertificateTrustScope API to control how custom certificates interact with default trusted certificates
• Custom Callbacks: Advanced customization using WithExecutableCertificateTrustCallback and WithContainerCertificateTrustCallback for fine-grained control

Practical Guidance

• Code examples for each major feature and API
• Common scenarios including enabling HTTPS telemetry to the dashboard, trusting custom certificates in containers, and configuring Python apps
• Limitations and considerations (run mode only, language/runtime support variations)
• Cross-references to related documentation

Example Usage

var builder = DistributedApplication.CreateBuilder(args);

// Create a certificate authority collection
var certBundle = builder.AddCertificateAuthorityCollection("my-bundle")
    .WithCertificates(myCertificates);

// Apply to resources that need to trust these certificates
builder.AddNpmApp("my-project", "../myapp")
    .WithCertificateAuthorityCollection(certBundle);

// Configure trust scope for Python apps
builder.AddPythonModule("api", "./api", "uvicorn")
    .WithCertificateTrustScope(CertificateTrustScope.System);

builder.Build().Run();

Documentation Standards

The article follows all Aspire documentation guidelines:

• Uses "Aspire" terminology (not ".NET Aspire")
• Sentence case headings
• Active voice, second person
• AI usage disclosed in frontmatter
• Passes markdownlint validation (0 errors)

Closes #5307

Original prompt

Please create a draft article that addresses issue @dotnet/docs-aspire/issues/5307 - the description provides plenty of detail, be sure to consider all of it. You do not need to callout the version that this feature was introduced.

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Internal previews

📄 File	🔗 Preview link
docs/app-host/certificate-trust.md	docs/app-host/certificate-trust
docs/toc.yml	docs/toc