Playground: Replace snake_case with camelCase

[FelixTJDietrich]

Motivation

Athena now also supports camelCase so we can change most of the properties in the Playground to this instead of snake_case. This is mostly for consistency reasons and for sticking more to a JS/TS programming style.

Description

Change all occurrences in the Playground from snake_case to camelCase, including the example data and the data export scripts, i.e. SQL query (?) (open for discussion).

Context:

Ah, I see: The problem is that our data models in TS also have underscores. Maybe we should do a PR in the future where we generally change this, considering that Athena now also accepts camelCase input values

Originally posted by @pal03377 in #61 (comment)