Document allowSubdomains field for web-to-app linking JSON configuration

[Copilot]

The allowSubdomains field in the web-to-app linking JSON configuration was missing from the documentation, despite being essential for subdomain support. Users registering both main domains (e.g., example.com) and wildcard subdomains (e.g., *.example.com) in their app manifest need this field to enable proper subdomain handling.

Problem:
Without allowSubdomains: true in the JSON file, subdomain links like fr.example.com/path would open in the browser instead of the app, even when the app manifest includes wildcard subdomain registration.

Changes:

• Added a new "Subdomain support" section explaining when and why the field is needed
• Included a complete JSON example demonstrating the allowSubdomains field usage
• Added a note in the "Multiple apps" section about including the field for each app entry
• Clarified that without this field, subdomain links will open in browser instead of the app

The documentation now provides complete guidance for developers who need subdomain support in their web-to-app linking configuration.

Fixes #4510.

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• maps.windows.com
  • Triggering command: curl -s REDACTED (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

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[learn-build-service-prod]

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[learn-build-service-prod]

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File	Status	Preview URL	Details
hub/apps/develop/launch/web-to-app-linking.md	✅Succeeded

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