[Release] update changelogs for 9.0 release

CHANGELOG.asciidoc

@@ -1,4 +1,5 @@
 // tag::list[]
+* <<apm-release-notes-9.0>>
 * <<apm-release-notes-8.17>>
 * <<apm-release-notes-8.16>>
 * <<apm-release-notes-8.15>>
@@ -21,6 +22,7 @@
 
 // tag::includes[]
 include::./changelogs/head.asciidoc[]
+include::./changelogs/9.0.asciidoc[]
 include::./changelogs/8.17.asciidoc[]
 include::./changelogs/8.16.asciidoc[]
 include::./changelogs/8.15.asciidoc[]

changelogs/9.0.asciidoc

@@ -0,0 +1,26 @@
+[[apm-release-notes-9.0]]
+== APM version 9.0
+* <<apm-release-notes-9.0.0>>
+
+[float]
+[[apm-release-notes-9.0.0]]
+=== APM version 9.0.0
+
+https://github.com/elastic/apm-server/compare/v\...v9.0.0[View commits]
+
+[float]
+==== Bug fixes
+- Fix overflow in validation of `apm-server.agent.config.cache.expiration` on 32-bit architectures {pull}15216[15216]
+
+[float]
+==== Breaking Changes
+
+[float]
+==== Deprecations
+
+[float]
+==== Intake API Changes
+
+[float]
+==== Added
+- Tail-based sampling: Storage layer is rewritten to use Pebble database instead of BadgerDB. The new implementation offers a substantial throughput increase while consuming significantly less memory. Disk usage is lower and more stable. See PR for benchmark details. {pull}15235[15235]

changelogs/head.asciidoc

@@ -1,14 +1,13 @@
 [[release-notes-head]]
 == APM version HEAD
 
-https://github.com/elastic/apm-server/compare/8.16\...8.x[View commits]
+https://github.com/elastic/apm-server/compare/9.0\...main[View commits]
 
 [float]
-==== Bug fixes
-- Fix overflow in validation of `apm-server.agent.config.cache.expiration` on 32-bit architectures {pull}15216[15216]
+==== Breaking Changes
 
 [float]
-==== Breaking Changes
+==== Bug fixes
 
 [float]
 ==== Deprecations
@@ -18,4 +17,3 @@ https://github.com/elastic/apm-server/compare/8.16\...8.x[View commits]
 
 [float]
 ==== Added
-- Tail-based sampling: Storage layer is rewritten to use Pebble database instead of BadgerDB. The new implementation offers a substantial throughput increase while consuming significantly less memory. Disk usage is lower and more stable. See PR for benchmark details. {pull}15235[15235]