Add release notes for 3.8.0 (#1905) (#1911)

(cherry picked from commit 8817f88)

Signed-off-by: opensearch-ci-bot <opensearch-infra@amazon.com>

Author: opensearch-ci-bot

release-notes/opensearch-neural-search.release-notes-3.8.0.0.md

@@ -0,0 +1,20 @@
+## Version 3.8.0 Release Notes
+
+Compatible with OpenSearch and OpenSearch Dashboards version 3.8.0
+
+### Enhancements
+
+* Allow custom field name for storing previous rerank score to avoid overwriting existing document fields ([#1880](https://github.com/opensearch-project/neural-search/pull/1880))
+* Improve hybrid query filter validation error message to provide guidance on combining multiple filters ([#1870](https://github.com/opensearch-project/neural-search/pull/1870))
+* Skip two-phase rescore optimization for queries containing sort fields ([#1898](https://github.com/opensearch-project/neural-search/pull/1898))
+
+### Bug Fixes
+
+* Block hybrid query execution with `dfs_query_then_fetch` search type to prevent incorrect results ([#1873](https://github.com/opensearch-project/neural-search/pull/1873))
+* Fix hybrid query explanation producing a single normalization block instead of per-sub-query blocks for indices with nested fields ([#1876](https://github.com/opensearch-project/neural-search/pull/1876))
+
+### Infrastructure
+
+* Fix Check Workflow Events CI job by adding `pr_review.yml` to the allowlist and removing stray YAML fragment ([#1901](https://github.com/opensearch-project/neural-search/pull/1901))
+* Fix flaky `HybridQueryExplainIT` explanation test by using per-document `_id` assertions ([#1900](https://github.com/opensearch-project/neural-search/pull/1900))
+* Onboard new backport-pr reusable GitHub workflow ([#1881](https://github.com/opensearch-project/neural-search/pull/1881))