Arcade: support importing custom dataset / schema

[m3hari]

Is there an existing issue for this?

• [x] I have searched the existing issues

Code of Conduct

• [x] I agree to follow this project's Code of Conduct

Feature Request

I wanted to provide a proper a sandbox link for an issue but it's difficult at the moment. If the arcade playground allow adding custom dataset and generate types on the fly, it will make it much easier to reproduce issues.