API updates for confirm data step in CSV file import.

[kgodey]

Problem

Our design for file import cannot be handled by our existing APIs, specifically the data confirmation step.

Proposed solution

We need API updates that allow the user to:

• Change column names (hopefully handled by Create a Column API #199)
• Change column types (hopefully handled by Create a Column API #199)
• Switch whether we use the first row as headers
• Choose which columns to import (drop columns)

Additional context

This issue involves a lot of changes to the architecture, so please write a technical spec on the wiki's Architecture section and get some feedback from @kgodey and @mathemancer before implementing this issue.

Please note that even though we have a table in the database at this point, we also have the actual data file stored on disk so we can access it if needed. We may want to do so while switching whether to use the first row as a header.

Blocked by #199, #200

[kgodey]

@pavish's comment from #199 seems more appropriate to discuss here.

@kgodey @mathemancer The Column API makes perfect sense for maintaining REST API standards.

Based on the UX, the user will make multiple modifications (change names, types etc.,) and then hit save. To make it easier for clients and to avoid multiple updates, I believe we will need another endpoint that batches column updates? Thoughts?

I see that there is a ticket already #201 for the data confirmation page, but we haven't specified anything about batching these column updates anywhere.

@pavish I think it would be easiest to use the Column API from #199 to make modifications one column at a time as the user makes them (before they press save), because each of them is a distinct ALTER operation in the database with its own errors. That way, we can also show the user a preview of what their column looks like as the new type.