✨ add type and sort columns to variables table

[Marigold]

Grapher part of adding indicator type to MySQL and adding ordinal type. Here's ETL pull request.

Fixes #1690

[Marigold]

@danyx23 we've agreed on using dimensions.values.values for ordinal variable categories, but @sophiamersmann had a good question about what this should look like in the database. This PR currently uses fields type and sort (specifically for storing an array of categories). We have a couple of options:

1. Don't store sort field in MySQL at all and keep it only in JSON
2. Keep it as it is
3. Change type field to JSON and store it as {"type": "ordinal", "sort": ["a", "b", "c"]} - this is future-proof and flexible

What do you think?

[Marigold]

There's another #2039 we had open back then. We should either merge them or simply kill the old one.

[sophiamersmann]

I copy-pasted the code that I needed from #2039 into this PR, so I'm happy for it to be killed

[danyx23]

I think the current approach is good @Marigold. We'll probably query the type field much more often than the sort field in the DB, so having the type field as a column makes sense to me.

[Marigold]

Thanks! @sophiamersmann I removed sort field from JSON and kept only dimensions.values.values there. Leaving this PR in your hands now. Once you merge it, I can merge the ETL part.

[marcelgerber]

Nice!
I didn't realize that this would be so easy, and that we can just write a drop-in replacement of sortedUniqNonEmptyStringVals.

Also, 👑 to Mojmir for setting up the staging server with the staging indicator, that was super helpful to see this in action.

[sophiamersmann]

Thanks for the review!

I pushed one more commit that updates Grapher's db types and asked Daniel to sign off on it. This is good to merge now, but I'll wait for the holidays to be over :)