Update JSON docs for new type

[gingerwizard]

Discussing with @melvynator we wont do this until GA.

General thought process around recommendations of JSON vs current approaches is as follows:

1. If user has only a 10s of columns which are largely static - as defined by the existing guide - https://clickhouse.com/docs/en/integrations/data-formats/json/schema#static-vs-dynamic-json then continue to use Tuples, Array and Nested. This enforces types and ensures garbage cannot be inserted + ensures optimal performance.
2. If 100s of columns + dynamic - use the JSON type but materialized if codecs required. (< 1024, all should be columns) 1000s of paths, highly dynamic - use JSON but materialized your key columns.