Add 0.8.0 release notes and bump up version (opensearch-project#162)

Signed-off-by: Karen Xu <karenxyr@gmail.com>

Author: karenyrx

CHANGELOG.md

@@ -6,10 +6,7 @@ Inspired from [Keep a Changelog](https://keepachangelog.com/en/1.0.0/)
 ### Added
 
 ### Changed
-- Align manual proto with generated proto - search ([#154](https://github.com/opensearch-project/opensearch-protobufs/pull/154))
-- Update preprocessing - convert oneof const to enum ([#157](https://github.com/opensearch-project/opensearch-protobufs/pull/157))
-- Align manual proto with generated proto - enums ([#158](https://github.com/opensearch-project/opensearch-protobufs/pull/158))
-- Refactor manual proto ResponseItem ([#160](https://github.com/opensearch-project/opensearch-protobufs/pull/160))
+
 ### Removed
 
 ### Fixed

release-notes/opensearch-protobufs.release-notes-0.8.0.md

@@ -0,0 +1,15 @@
+## Version 0.8.0 (2025-08-09) Release Notes
+
+### Added
+
+### Changed
+- Align manual proto with generated proto - search ([#154](https://github.com/opensearch-project/opensearch-protobufs/pull/154))
+- Update preprocessing - convert oneof const to enum ([#157](https://github.com/opensearch-project/opensearch-protobufs/pull/157))
+- Align manual proto with generated proto - enums ([#158](https://github.com/opensearch-project/opensearch-protobufs/pull/158))
+- Refactor manual proto ResponseItem ([#160](https://github.com/opensearch-project/opensearch-protobufs/pull/160))
+
+### Removed
+
+### Fixed
+
+### Security