fix(options): set scheduledTasks to an empty object by default

[noook]

🔗 Linked issue

Fixes #2283, related to nuxt/devtools#626

❓ Type of change

• 📖 Documentation (updates to the documentation, readme, or JSdoc annotations)
• 🐞 Bug fix (a non-breaking change that fixes an issue)
• 👌 Enhancement (improving an existing functionality like performance)
• ✨ New feature (a non-breaking change that adds functionality)
• 🧹 Chore (updates to the build process or auxiliary tools and libraries)
• ⚠️ Breaking change (fix or feature that would cause existing functionality to change)

📚 Description

Nitro config types indicate that nitro.options.scheduledTasks should always be an object, empty or not. This PR makes the property an empty object as default as opposed to undefined which is not assignable to

scheduledTasks: { [cron: string]: string | string[] }

📝 Checklist

• I have linked an issue or discussion.
• I have updated the documentation accordingly.