Export the instance configuration as a deployment template

Generates a downloadable infrastructure-as-code template for the instance configuration ("Download template" on the instance creation wizard review step). The template captures the UI-visible provisioning inputs — name, region, availability zone, image, architecture, authentication settings (never secret material), OS disk type/size, encryption, network bindings (VNet/subnet/public IP/NSG), accelerated networking, managed identity, boot diagnostics, monitoring, backup, auto-shutdown schedule, and user data — so the deployment can be repeated. Read-only with respect to the instance: no resource state is mutated. Validation: instance must exist and be visible in the active scope → 404 NOT_FOUND; format (when provided) must be one of [json, yaml] → 422 VALIDATION_FAILED. Errors: 401 UNAUTHENTICATED; 403 FORBIDDEN when the caller lacks read access to the scope; 404 NOT_FOUND for an unknown instanceId; 422 VALIDATION_FAILED for an unsupported format; 500 INTERNAL. Async & state: Synchronous (200) returning the rendered template document inline; no state change and no SSE frames. Idempotency/Concurrency: This operation does not use Idempotency-Key; it may be omitted and a sent one is ignored. Generation is deterministic for a given instance revision: repeated calls return the same content, with a fresh generatedAt each time. No If-Match applies.