Add license mention to ESQL categorize

exceptional licensing mention in docs

Author: leemthompo

docs/reference/query-languages/esql/functions-operators/grouping-functions.md

@@ -16,6 +16,9 @@ The [`STATS`](/reference/query-languages/esql/commands/processing-commands.md#es
 :::{include} ../_snippets/functions/layout/bucket.md
 :::
 
+:::{note} The `CATEGORIZE` function requires a platinum license
+:::
+
 :::{include} ../_snippets/functions/layout/categorize.md
 :::