Use Korro in samples on the Kotlin website

Follow up of #987.

The Kotlin website contains code samples demonstrating usage of DataFrame, Kandy. We need to use Korro to verify these samples.

One of the pages with the samples: https://kotlinlang.org/docs/data-analysis-connect-to-db.html.

There might be other pages, we need to get to this issue and clarify it more precisely in the second half of June when the website content is clearer.

Start with the samples on the Kotlin website page data-analysis-connect-to-db.html and identify the other DataFrame and Kandy sample pages in scope. Use Korro to verify the samples, with completion meaning the relevant website samples pass verification; the issue notes that the precise scope still needs clarification.

Written by the indexing model from the issue text.