changelog: update 8.15 missing changelog entry (#14909)

(cherry picked from commit 2a9a9a1)

changelogs/8.15.asciidoc

@@ -101,9 +101,10 @@ https://github.com/elastic/apm-server/compare/v8.14.3\...v8.15.0[View commits]
 
 - Add `elasticsearch.flushed.uncompressed.bytes` metric {pull}13155[13155]
 - APM Server now relies on the Elasticsearch apm-data plugin's index templates, removing the requirement to install the APM integration package {pull}12066[12066]
+- Switch the default lifecycle management to leverage DSL instead of ILM, the change is executed as a part of Elasticsearch apm-data plugin migration {pull}12066[12066]
 - Upgraded bundled APM Java agent attacher CLI to version 1.50.0 {pull}13326[13326]
 - Enable Kibana curated UIs to work with hostmetrics from OpenTelemetry's https://pkg.go.dev/go.opentelemetry.io/collector/receiver/hostmetricsreceiver[hostmetricsreceiver] {pull}13196[13196]
 - Add require data stream to bulk index requests {pull}13398[13398]
 - Support self-instrumentation when in managed mode by getting tracing configs via reloader {pull}13514[13514] {pull}13653[13653] {pull}13691[13691] {pull}13790[13790]
 - Add mapping for OpenTelemetry attribute `messaging.destination.name` to derive `service.target` correctly {pull}13472[13472]
-- APM Server now automatically retries document-level 429s from Elasticsearch to avoid dropping data. `output.elasticsearch.max_retries` now controls both request-level and document-level retries, and defaults to `3`. {pull}13620[13620]
+- APM Server now automatically retries document-level 429s from Elasticsearch to avoid dropping data. `output.elasticsearch.max_retries` now controls both request-level and document-level retries, and defaults to `3`. {pull}13620[13620]