Support remote Bicep template URLs in `rad deploy`

[zachcasper]

Overview of feature request

Add support for using a remote Bicep template URL with rad deploy, specifically allowing commands such as rad deploy https://github.com/radius-project/resource-types-contrib/files/recipe-packs/azure/aks-recipepack.bicep to resolve and deploy the referenced file. The command should retrieve or otherwise resolve the remote file before compiling and deploying it, while preserving the existing behavior for local .bicep and .json files. kubectl already supports deploying resources from remote URLs today, so rad deploy should provide similar behavior for remote Bicep templates.

Acceptance criteria

• The example HTTPS URL resolves and proceeds through Bicep compilation and deployment.
• Remote template resolution reports clear errors for invalid URLs, unavailable files, and download or access failures.
• Existing local .bicep and .json deployment workflows continue to work unchanged.
• Relative imports or other file dependencies used by the retrieved Bicep template are handled correctly, or are explicitly rejected with a clear error message.
• URL handling follows behavior users already expect from tools such as kubectl.

Additional context

The current rad deploy implementation treats its positional template argument as a local filesystem path. The requested behavior is to accept a HTTPS URL directly. Example: rad deploy https://github.com/radius-project/resource-types-contrib/files/recipe-packs/azure/aks-recipepack.bicep.

[radius-triage]

👋 @zachcasper Thanks for filing this feature request.

A project maintainer will review this feature request and get back to you soon.

We also welcome community contributions! If you would like to pick this item up sooner and submit a pull request, please visit our contribution guidelines and assign this to yourself by commenting "/assign" on this issue.

For more information on our triage process please visit our triage overview