Add Changelog entry

Signed-off-by: gouthamve <gouthamve@gmail.com>

CHANGELOG.md

@@ -12,6 +12,9 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
 
 - Add the new `go.opentelemetry.io/contrib/instrgen` package to provide auto-generated source code instrumentation. (#3068, #3108)
 - `NewSDK` in `go.opentelemetry.io/contrib/config` now returns a configured SDK with a valid `MeterProvider`. (#4804)
+- Add an EXPERIMENTAL `OTEL_METRICS_PRODUCERS` environment variable to `go.opentelemetry.io/contrib/autoexport` to be set metrics producers. (#5281)
+  -  Only `prometheus` is a supported value for now.
+  - `WithFallbackMetricProducer(func(context.Context) (metric.Producer, error))` allows adding a fallback option if the env var is not set.
 
 ## [1.25.0/0.50.0/0.19.0/0.5.0/0.0.1] - 2024-04-05