feat(openapi): support configuration via openapi

[hanspagel]

WIP need to update the dependency to fix the build

🔗 Linked issue

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❓ 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

1. This PR makes the OpenAPI endpoint configurable (title, description, version). It’s still possible to just pass experimental.openAPI: true, but you can also pass an object. This should make it a non-breaking addition.

2. With this PR you can also pass a configuration for Scalar (eg. to use other themes). It’s optional, but enables users to use a ton of powerful features. More on this here: https://github.com/scalar/scalar?tab=readme-ov-file#configuration

3. This PR removes the Scalar proxy. It’s really helpful to avoid CORS issues when using the API client, but you can’t use an external proxy to send request to localhost, so it’s not really helpful for local development.

Note: This PR also adds @scalar/api-reference as a dev dependency, just to import the configuration type for convenience. We could also remove it and just allow AnyObject (not so helpful, though), copy the type to the package (which might be outdated quickly) or we move our types to a separate package. It seems to break the build, we definitely need to change this. What route should we take? 🤔

I’d love to add some tests, too, but haven’t looked into that yet. That’s why I submitted it as a draft for now.

Any kind of feedback is really appreciated! We’re eager to make the OpenAPI stuff really great for everyone.

📝 Checklist

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