Add header=colId option to thedownload/table-schema route

[vviers]

Following up on #692, it would be quite useful for us to be able to retrieve the table-schema of a table with its column ids instead of labels !
This would make our ETL much more robust :)

Cheers !

[alexmojaki]

I don't understand this. What does download/table-schema mean?

I do think it would be good if GET /tables and even more so the endpoint in #716 included the metadata about the columns of each table, like GET /columns but filtered/grouped by table.

[paulfitz]

I don't understand this. What does download/table-schema mean?

It is an endpoint that provides metadata about a table in a standard format (https://specs.frictionlessdata.io/table-schema/). There's some context at #423.

[fflorent]

@vviers You assigned you and me on this issue, flagged it as good-first-issue. How do you intend to work on this? Pair-programming maybe? :)

[vviers]

I'd say whoever has time to do it first does it first :) (i'm also happy to pair prog next week)

[paulfitz]

It would be good to add the download/table-schema endpoint to https://github.com/gristlabs/grist-help/blob/master/api/grist.yml since it could be helpful to others.