Apply custom response config to the webhook response at runtime

[theroinaochieng]

User story

When a sync-mode webhook run completes, the response currently returns a fixed 201 with the full final state. We need to check whether the trigger has custom response config and, if so, use those values to shape the HTTP response instead.

User acceptance criteria

1. Hardcoded status codes and bodies are returned correctly when set.
2. state.* dot-path expressions are resolved against the final run state.
3. If a path fails to resolve, the default sync response is returned.
4. The existing default sync response behaviour is fully preserved when no custom config is set.