Check for consistent usage of old and new JSON terminology

[Blargian]

See https://clickhouse-inc.slack.com/archives/C03A9B0H05T/p1747416076505979 for context.

Task:

• Go through the docs and make sure that "JSON" always refers to the new type.
• We refer to the old JSON as "Object Data Type" and mark it as deprecated where necessary.

A grep for JSON through the docs can produce pages to check.