Forward port release notes for v8.16.4 (#122288)

* Forward port release notes for v8.16.4

* Apply suggestions from code review

---------

Co-authored-by: Liam Thompson <32779855+leemthompo@users.noreply.github.com>

docs/reference/migration/migrate_8_16.asciidoc

@@ -9,6 +9,8 @@ your application to {es} 8.16.
 
 See also <<release-highlights>> and <<es-release-notes>>.
 
+
+
 [discrete]
 [[breaking-changes-8.16]]
 === Breaking changes

docs/reference/release-notes.asciidoc

@@ -10,6 +10,7 @@ This section summarizes the changes in each release.
 * <<release-notes-8.18.0>>
 * <<release-notes-8.17.1>>
 * <<release-notes-8.17.0>>
+* <<release-notes-8.16.4>>
 * <<release-notes-8.16.3>>
 * <<release-notes-8.16.2>>
 * <<release-notes-8.16.1>>
@@ -87,6 +88,7 @@ include::release-notes/8.19.0.asciidoc[]
 include::release-notes/8.18.0.asciidoc[]
 include::release-notes/8.17.1.asciidoc[]
 include::release-notes/8.17.0.asciidoc[]
+include::release-notes/8.16.4.asciidoc[]
 include::release-notes/8.16.3.asciidoc[]
 include::release-notes/8.16.2.asciidoc[]
 include::release-notes/8.16.1.asciidoc[]

docs/reference/release-notes/8.16.4.asciidoc

@@ -0,0 +1,42 @@
+[[release-notes-8.16.4]]
+== {es} version 8.16.4
+
+Also see <<breaking-changes-8.16,Breaking changes in 8.16>>.
+
+[[bug-8.16.4]]
+[float]
+=== Bug fixes
+
+Aggregations::
+* Aggregations cancellation after collection {es-pull}120944[#120944] (issue: {es-issue}108701[#108701])
+
+Data streams::
+* Map `scope.name` as a dimension {es-pull}120590[#120590]
+
+ES|QL::
+* Use `field_caps` native nested fields filtering {es-pull}117201[#117201] (issue: {es-issue}117054[#117054])
+
+Mapping::
+* Fix synthetic source issue with deeply nested ignored source fields {es-pull}121715[#121715]
+
+Ranking::
+* Fix LTR rescorer throws 'local model reference is null' on multi-shards index when explained is enabled {es-pull}120717[#120717] (issue: {es-issue}120739[#120739])
+* LTR sometines throw `NullPointerException:` Cannot read field "approximation" because "top" is null {es-pull}120809[#120809]
+* Normalize negative scores for `text_similarity_reranker` retriever {es-pull}120930[#120930] (issue: {es-issue}120201[#120201])
+* Update Text Similarity Reranker to Properly Handle Aliases {es-pull}120062[#120062] (issue: {es-issue}119617[#119617])
+
+Search::
+* Fix potential file leak in ES816BinaryQuantizedVectorsWriter {es-pull}120014[#120014] (issue: {es-issue}119981[#119981])
+
+Snapshot/Restore::
+* Cheaper snapshot-related `toString()` impls {es-pull}121283[#121283]
+* Issue S3 web identity token refresh call with sufficient permissions {es-pull}119748[#119748] (issue: {es-issue}119747[#119747])
+
+[[enhancement-8.16.4]]
+[float]
+=== Enhancements
+
+Ingest Node::
+* Improve memory aspects of enrich cache {es-pull}120256[#120256] (issues: {es-issue}96050[#96050], {es-issue}120021[#120021])
+
+

docs/reference/release-notes/highlights.asciidoc

@@ -33,13 +33,37 @@ Other versions:
 
 endif::[]
 
-// The notable-highlights tag marks entries that
-// should be featured in the Stack Installation and Upgrade Guide:
 // tag::notable-highlights[]
-// [discrete]
-// === Heading
-//
-// Description.
+
+[discrete]
+[[add_new_experimental_rank_vectors_mapping_for_late_interaction_second_order_ranking]]
+=== Add new experimental `rank_vectors` mapping for late-interaction second order ranking
+Late-interaction models are powerful rerankers. While their size and overall cost doesn't lend itself for HNSW indexing, utilizing them as second order reranking can provide excellent boosts in relevance. The new `rank_vectors` mapping allows for rescoring over new and novel multi-vector late-interaction models like ColBERT or ColPali.
+
+{es-pull}118804[#118804]
+
+[discrete]
+[[8_x_add_new_experimental_rank_vectors_mapping_for_late_interaction_second_order_ranking]]
+=== [8.x] Add new experimental `rank_vectors` mapping for late-interaction second order ranking
+Backports the following commits to 8.x:  - Add new experimental
+rank_vectors mapping for late-interaction second order ranking (#118804)
+
+{es-pull}119601[#119601]
+
+[discrete]
+[[enable_lookup_join_in_non_snapshot_builds]]
+=== Enable LOOKUP JOIN in non-snapshot builds
+This effectively releases LOOKUP JOIN into tech preview. Docs will
+follow in a separate PR.
+
+- Enable the lexing/grammar for LOOKUP JOIN in non-snapshot builds.
+- Remove the grammar for the unsupported `| JOIN ...` command (without `LOOKUP` as first keyword). The way the lexer modes work, otherwise we'd also have to enable `| JOIN ...` syntax on non-snapshot builds and would have to add additional validation to provide appropriate error messages.
+- Remove grammar for `LOOKUP JOIN index AS ...` because qualifiers are not yet supported. Otherwise we'd have to put in additional validation as well to prevent such queries.
+
+Also fix https://github.com/elastic/elasticsearch/issues/121185
+
+{es-pull}121193[#121193]
+
 // end::notable-highlights[]