(Doc+) Clarify dimension field requirements for time_series aggregation (#119442)

* (Doc+) Clarify dimension field requirements for time_series aggregation

👋 howdy, team!

This PR adds a note explaining that time series indices require:
- index.mode set to "time_series"
- at least one dimension field with time_series_dimension: true
- a routing_path array listing those dimension fields

Without these settings, the time_series aggregation may return empty buckets or behave unexpectedly. By emphasizing the dimension field requirement, we help users configure their time series indices correctly and see meaningful aggregation results.

* Apply suggestions from code review

Co-authored-by: shainaraskas <[email protected]>

---------

Co-authored-by: Liam Thompson <[email protected]>
Co-authored-by: shainaraskas <[email protected]>
(cherry picked from commit e120739)

Author: 3 people

docs/reference/aggregations/bucket/time-series-aggregation.asciidoc

@@ -6,9 +6,14 @@
 
 preview::[]
 
-The time series aggregation queries data created using a time series index. This is typically data such as metrics
+The time series aggregation queries data created using a <<tsds,Time series data stream (TSDS)>>. This is typically data such as metrics
 or other data streams with a time component, and requires creating an index using the time series mode.
 
+[NOTE]
+====
+Refer to the <<differences-from-regular-data-stream, TSDS documentation>> to learn more about the key differences from regular data streams.
+====
+
 //////////////////////////
 
 Creating a time series mapping