Regenerate release notes after version bump 8.4.0

And after forward porting 8.3.0 release notes changes.

Author: craigtaverner

docs/changelog/87235.yaml

@@ -1,10 +1,12 @@
 include::migration_intro.asciidoc[]
 
+* <<migrating-8.4,Migrating to 8.4>>
 * <<migrating-8.3,Migrating to 8.3>>
 * <<migrating-8.2,Migrating to 8.2>>
 * <<migrating-8.1,Migrating to 8.1>>
 * <<migrating-8.0,Migrating to 8.0>>
 
+include::migrate_8_4.asciidoc[]
 include::migrate_8_3.asciidoc[]
 include::migrate_8_2.asciidoc[]
 include::migrate_8_1.asciidoc[]

docs/reference/migration/index.asciidoc

@@ -0,0 +1,64 @@
+[[migrating-8.4]]
+== Migrating to 8.4
+++++
+<titleabbrev>8.4</titleabbrev>
+++++
+
+This section discusses the changes that you need to be aware of when migrating
+your application to {es} 8.4.
+
+See also <<release-highlights>> and <<es-release-notes>>.
+
+coming::[8.4.0]
+
+
+[discrete]
+[[breaking-changes-8.4]]
+=== Breaking changes
+
+// tag::notable-breaking-changes[]
+There are no breaking changes in {es} 8.4.
+// end::notable-breaking-changes[]
+
+
+[discrete]
+[[deprecated-8.4]]
+=== Deprecations
+
+The following functionality has been deprecated in {es} 8.4
+and will be removed in a future version.
+While this won't have an immediate impact on your applications,
+we strongly encourage you take the described steps to update your code
+after upgrading to 8.4.
+
+To find out if you are using any deprecated functionality,
+enable <<deprecation-logging, deprecation logging>>.
+
+
+[discrete]
+[[deprecations_84_cluster_and_node_setting]]
+==== Cluster and node setting deprecations
+
+[[configuring_bind_dn_in_an_ldap_or_active_directory_ad_realm_without_corresponding_bind_password_deprecated]]
+.Configuring a bind DN in an LDAP or Active Directory (AD) realm without a corresponding bind password is deprecated
+[%collapsible]
+====
+*Details* +
+For LDAP or AD authentication realms, setting a bind DN (via the
+`xpack.security.authc.realms.ldap.*.bind_dn` realm setting) without a
+bind password is a misconfiguration that may prevent successful
+authentication to the node. In the next major release, nodes will fail
+to start if a bind DN is specified without a password.
+
+*Impact* +
+If you have a bind DN configured for an LDAP or AD authentication
+realm, set a bind password for {ref}/ldap-realm.html#ldap-realm-configuration[LDAP]
+or {ref}/active-directory-realm.html#ad-realm-configuration[Active Directory].
+Configuring a bind DN without a password generates a warning in the
+deprecation logs.
+
+*Note:* This deprecation only applies if your current LDAP or AD
+configuration specifies a bind DN without a password. This scenario is
+unlikely, but might impact a small subset of users.
+====
+

docs/reference/migration/migrate_8_4.asciidoc

@@ -6,6 +6,7 @@
 
 This section summarizes the changes in each release.
 
+* <<release-notes-8.4.0>>
 * <<release-notes-8.3.0>>
 * <<release-notes-8.2.3>>
 * <<release-notes-8.2.2>>
@@ -25,6 +26,7 @@ This section summarizes the changes in each release.
 
 --
 
+include::release-notes/8.4.0.asciidoc[]
 include::release-notes/8.3.0.asciidoc[]
 include::release-notes/8.2.3.asciidoc[]
 include::release-notes/8.2.2.asciidoc[]