Support Apache Arrow in DataBaseClient Specification

[domoritz]

https://observablehq.com/@observablehq/database-client-specification should support Apache Arrow tables. Arrow tables can be streaming so it would be a perfect fit for the format.

[ananya-roy]

#352

[domoritz]

Thank you for adding the link to #352. This request is similar but not the same. It's to support Arrow in the specification and not just the implementation. I imagine the specification could say something like "A function MAY return an Arrow Table instead of an array of objects."

[ananya-roy]

Thanks for clarifying