[DOCS] test/example data: fix unknown json schema

[jkowalleck]

while i was updating some test resources, I noticed that my IDE did not autocomplete in the JSON files, but did so in the XML files.
I noticed, that this was caused by the missing $schema assignment in the JSON files.

options to fix this:

• add IDE hints that files in a certain folder should match a certain schema
• add the appropriate $schema in every JSON file

latter one is preferred.