[main] [DOCS] Time series indices support non-metric/dimension fields (#99709) (#99811)

Co-authored-by: James Rodewig <james.rodewig@elastic.co>
Co-authored-by: Gilad Gal <gilad.gal@elastic.co>

docs/reference/data-streams/tsds.asciidoc

@@ -56,6 +56,8 @@ documents, the document `_id` is a hash of the document's dimensions and
 * A TSDS uses <<synthetic-source,synthetic `_source`>>, and as a result is
 subject to a number of <<synthetic-source-restrictions,restrictions>>.
 
+NOTE: A time series index can contain fields other than dimensions or metrics.
+
 [discrete]
 [[time-series]]
 === What is a time series?