add changelog entries

Author: juliuskoval

src/OpenTelemetry.Api/CHANGELOG.md

@@ -6,6 +6,9 @@ Notes](../../RELEASENOTES.md).
 
 ## Unreleased
 
+* Added `ObservedTimestamp` property to `LogRecordData`.
+  ([#6979](https://github.com/open-telemetry/opentelemetry-dotnet/pull/6979))
+
 ## 1.15.1
 
 Released 2026-Mar-27

src/OpenTelemetry/CHANGELOG.md

@@ -6,6 +6,9 @@ Notes](../../RELEASENOTES.md).
 
 ## Unreleased
 
+* Added `ObservedTimestamp` property to `LogRecord`.
+  ([#6979](https://github.com/open-telemetry/opentelemetry-dotnet/pull/6979))
+
 ## 1.15.1
 
 Released 2026-Mar-27