Clarify update operations may be performed on a data stream's backing…

… indices (elastic#105408) (elastic#105416)

These statements come off a little too strongly towards "don't use data streams if you *ever* have updates", but they do support updates when necessary, as long as the backing indices are used.

(cherry picked from commit d95d6ad)

docs/reference/alias.asciidoc

@@ -240,8 +240,9 @@ POST _aliases
 include::{es-repo-dir}/indices/aliases.asciidoc[tag=write-index-defaults]
 
 TIP: We recommend using data streams to store append-only time series data. If
-you frequently update or delete existing time series data, use an index alias
-with a write index instead. See
+you need to update or delete existing time series data, you can perform update or delete operations
+directly on the data stream backing index. If you frequently send multiple documents using the same
+`_id` expecting last-write-wins, you may want to use an index alias with a write index instead. See
 <<manage-time-series-data-without-data-streams>>.
 
 [discrete]

docs/reference/ilm/ilm-tutorial.asciidoc

@@ -14,11 +14,11 @@ requirements for your newest data, control costs over time, enforce retention po
 and still get the most out of your data.
 
 TIP: Data streams are best suited for
-<<data-streams-append-only,append-only>> use cases. If you need to frequently
-update or delete existing documents across multiple indices, we recommend
-using an index alias and index template instead. You can still use ILM to
-manage and rollover the alias's indices. Skip to
-<<manage-time-series-data-without-data-streams>>.
+<<data-streams-append-only,append-only>> use cases. If you need to update or delete existing time
+series data, you can perform update or delete operations directly on the data stream backing index.
+If you frequently send multiple documents using the same `_id` expecting last-write-wins, you may
+want to use an index alias with a write index instead. You can still use ILM to manage and rollover
+the alias's indices. Skip to <<manage-time-series-data-without-data-streams>>.
 
 To automate rollover and management of a data stream with {ilm-init}, you: