docs: Update changelogs for 8.12 release (#12220)

CHANGELOG.asciidoc

@@ -1,4 +1,4 @@
-include::./changelogs/head.asciidoc[]
+include::./changelogs/8.12.asciidoc[]
 include::./changelogs/8.11.asciidoc[]
 include::./changelogs/8.10.asciidoc[]
 include::./changelogs/8.9.asciidoc[]

changelogs/head.asciidoc → changelogs/8.12.asciidoc

@@ -1,7 +1,13 @@
-[[release-notes-head]]
-== APM version HEAD
+[[release-notes-8.12]]
+== APM version 8.12
 
-https://github.com/elastic/apm-server/compare/8.11\...main[View commits]
+https://github.com/elastic/apm-server/compare/8.11\...8.12[View commits]
+
+* <<release-notes-8.12.0>>
+
+[float]
+[[release-notes-8.12.0]]
+=== APM version 8.12.0
 
 [float]
 ==== Breaking Changes
@@ -12,12 +18,6 @@ https://github.com/elastic/apm-server/compare/8.11\...main[View commits]
 ==== Bug fixes
 - Switch built-in ILM rollover policies from max_size to max_primary_shard_size {pull}11729[11729].
 
-[float]
-==== Deprecations
-
-[float]
-==== Intake API Changes
-
 [float]
 ==== Added
 - Update container base image to Ubuntu 22.04 {pull}11778[11778]