Note discovery-file's deprecation in release notes (#33259)

This change adds a note about the deprecation of the `discovery-file` plugin to
the release docs for 6.5. Relates #33257

Author: DaveCTurner

docs/reference/release-notes.asciidoc

@@ -5,6 +5,7 @@
 --
 This section summarizes the changes in each release.
 
+* <<release-notes-6.5.0>>
 * <<release-notes-6.4.1>>
 * <<release-notes-6.4.0>>
 * <<release-notes-6.3.2>>
@@ -32,6 +33,7 @@ This section summarizes the changes in each release.
 
 --
 
+include::release-notes/6.5.asciidoc[]
 include::release-notes/6.4.asciidoc[]
 include::release-notes/6.3.asciidoc[]
 include::release-notes/6.2.asciidoc[]

docs/reference/release-notes/6.5.asciidoc

@@ -0,0 +1,94 @@
+////
+// To add a release, copy and paste the following text,  uncomment the relevant
+// sections, and add a link to the new section in the list of releases in
+// ../release-notes.asciidoc. Note that release subheads must be floated and
+// sections cannot be empty.
+// TEMPLATE
+
+// [[release-notes-n.n.n]]
+// == {es} n.n.n
+
+// coming[n.n.n]
+
+// Also see <<breaking-changes-n.n>>.
+
+// [float]
+// [[breaking-n.n.n]]
+// === Breaking Changes
+
+// [float]
+// [[breaking-java-n.n.n]]
+// === Breaking Java Changes
+
+// [float]
+// [[deprecation-n.n.n]]
+// === Deprecations
+
+// [float]
+// [[feature-n.n.n]]
+// === New Features
+
+// [float]
+// [[enhancement-n.n.n]]
+// === Enhancements
+
+// [float]
+// [[bug-n.n.n]]
+// === Bug Fixes
+
+// [float]
+// [[regression-n.n.n]]
+// === Regressions
+
+// [float]
+// === Known Issues
+////
+
+[[release-notes-6.5.0]]
+== {es} 6.5.0
+
+coming[6.5.0]
+
+Also see <<breaking-changes-6.5>>.
+
+// [float]
+// [[breaking-6.5.0]]
+// === Breaking Changes
+
+[float]
+[[breaking-java-6.5.0]]
+=== Breaking Java Changes
+
+Discovery-Plugins::
+* File-based discovery moved out of the `discovery-file` plugin and into core
+Elasticsearch {pull}33241[#33241] (issue: {issue}33030[#33030])
+
+// [float]
+// [[deprecation-6.5.0]]
+// === Deprecations
+
+Discovery-Plugins::
+* The `discovery-file` plugin is deprecated. Additionally, the expected
+location of the hosts file has moved from
+`$ES_PATH_CONF/discovery-file/unicast_hosts.txt` to
+`$ES_PATH_CONF/unicast_hosts.txt`, and the former location is deprecated.
+{pull}33241[#33241] (issue: {issue}33030[#33030])
+
+// [float]
+// [[feature-6.5.0]]
+// === New Features
+
+// [float]
+// [[enhancement-6.5.0]]
+// === Enhancements
+
+// [float]
+// [[bug-6.5.0]]
+// === Bug Fixes
+
+// [float]
+// [[regression-6.5.0]]
+// === Regressions
+
+// [float]
+// === Known Issues