[8.6] [DOCS] Fixes typo in admonition block (#93657)

* [8.6][DOCS] Adds admonition to frequent items agg docs about the renaming.

* [8.6] Fixes typo in admonition block.

Author: szabosteve

docs/reference/aggregations/bucket/frequent-items-aggregation.asciidoc

@@ -6,7 +6,7 @@
 
 experimental::[]
 
-IMPORTANT: This aggregation is renamed to `frequent item sets` in 8.7.
+IMPORTANT: This aggregation has been renamed to `frequent item sets` in 8.7.
 
 A bucket aggregation which finds frequent item sets. It is a form of association 
 rules mining that identifies items that often occur together. Items that are