Enable network access in a Shopify Function and call an external API for dynamic discount configuration

Verified steps

1. In shopify.extension.toml add [network_access] enabled = true; also declare any specific allowed domains under the network access config if the current TOML schema supports domain whitelisting — check current docs
2. In your Function's run entrypoint use the fetch API (available in the Function runtime) to call your external endpoint; pass any required auth headers and a short timeout appropriate for the Function's time budget
3. Design your external API to respond fast (well under the Function timeout budget documented by Shopify); cache configuration data at your API layer to avoid cold-start latency hitting Function timeouts
4. Handle fetch failures gracefully: if the external call fails, return a safe default result (e.g., no discount) rather than throwing, so checkout is not blocked by an API outage
5. Validate the response from your external API before using it in discount logic; malformed or unexpected data should log an error and fall back to a safe default
6. Test with network access enabled using `shopify app function run` with a sample input that exercises the network call path; confirm that timeout and error cases return valid FunctionRunResult shapes