docs: Update changelogs for 8.18 release (#15470)

Co-authored-by: obltmachine <[email protected]>
(cherry picked from commit 711b3e6)

# Conflicts:
#	changelogs/head.asciidoc

CHANGELOG.asciidoc

@@ -1,4 +1,5 @@
 // tag::list[]
+* <<apm-release-notes-8.18>>
 * <<apm-release-notes-8.17>>
 * <<apm-release-notes-8.16>>
 * <<apm-release-notes-8.15>>
@@ -20,7 +21,7 @@
 // end::list[]
 
 // tag::includes[]
-include::./changelogs/head.asciidoc[]
+include::./changelogs/8.18.asciidoc[]
 include::./changelogs/8.17.asciidoc[]
 include::./changelogs/8.16.asciidoc[]
 include::./changelogs/8.15.asciidoc[]

changelogs/8.18.asciidoc

@@ -0,0 +1,26 @@
+[[apm-release-notes-8.18]]
+== APM version 8.18
+* <<apm-release-notes-8.18.0>>
+
+[float]
+[[apm-release-notes-8.18.0]]
+=== APM version 8.18.0
+
+https://github.com/elastic/apm-server/compare/v8.17.1\...v8.18.0[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

@@ -1,15 +1,22 @@
 [[release-notes-head]]
 == APM version HEAD
 
+<<<<<<< HEAD
 https://github.com/elastic/apm-server/compare/8.17\...8.x[View commits]
 
 [float]
 ==== Bug fixes
 - Fix overflow in validation of `apm-server.agent.config.cache.expiration` on 32-bit architectures {pull}15216[15216]
+=======
+https://github.com/elastic/apm-server/compare/8.18\...8.x[View commits]
+>>>>>>> 711b3e6f (docs: Update changelogs for 8.18 release (#15470))
 
 [float]
 ==== Breaking Changes
 
+[float]
+==== Bug fixes
+
 [float]
 ==== Deprecations