add changelog

Author: cijothomas

opentelemetry-sdk/CHANGELOG.md

@@ -48,7 +48,15 @@
   - [2291](https://github.com/open-telemetry/opentelemetry-rust/pull/2291) Rename `logs_level_enabled flag` to `spec_unstable_logs_enabled`. Please enable this updated flag if the feature is needed. This flag will be removed once the feature is stabilized in the specifications.
 
 
-- **BREAKING**: `Temporality` enum moved from `opentelemetry_sdk::metrics::data::Temporality` to `opentelemetry_sdk::metrics::Temporality`.
+- **BREAKING**: `Temporality` enum moved from
+  `opentelemetry_sdk::metrics::data::Temporality` to
+  `opentelemetry_sdk::metrics::Temporality`.
+- Added a new `PeriodicReader` implementation (`PeriodicReaderWithOwnThread`)
+  that does not rely on async time, and instead creates own Thread. This is
+  under feature flag "experimental_metrics_periodic_reader_no_runtime". The
+  functionality maybe moved into existing PeriodReader or even removed in the
+  future. As of today, this cannot be used as-is with OTLP Metric Exporter or
+  any exporter requiring async runtimes.
 
 ## v0.26.0
 Released 2024-Sep-30