add changelog entry for schema v1.0.0 upgrade

Assisted-by: Claude Sonnet 4.6

Author: MikeGoldsmith

CHANGELOG.md

@@ -18,6 +18,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   ([#4958](https://github.com/open-telemetry/opentelemetry-python/pull/4958))
 - `opentelemetry-sdk`: fix type annotations on `MetricReader` and related types
   ([#4938](https://github.com/open-telemetry/opentelemetry-python/pull/4938/))
+- `opentelemetry-sdk`: upgrade vendored OTel configuration schema from v1.0.0-rc.3 to v1.0.0
+  ([#4965](https://github.com/open-telemetry/opentelemetry-python/pull/4965))
 
 ## Version 1.40.0/0.61b0 (2026-03-04)