Change structure of columns metadata

[seancolsen]

For my work on the table page, I need some changes to the way we handle columns metadata through the API.

I basically need all the same changes that I performed in #3672, but done for columns instead of tables.

[seancolsen]

@Anish9901 I've assigned you to this. Do you think you could pause work on the explorations-related APIs and switch over to this? Do you need any additional detail? Or is my description above clear enough? I think if you read over the commits I made in #3672 it should hopefully make sense.

[Anish9901]

Yes, I could switch over to this. Your description is clear enough, I'll ask for more details if I need any.