Add 2.15.0 release notes (#639)

Signed-off-by: Prudhvi Godithi <pgodithi@amazon.com>

release-notes/opensearch-job-scheduler.release-notes-2.15.0.0.md

@@ -0,0 +1,11 @@
+## Version 2.14.0.0
+
+Compatible with OpenSearch 2.14.0
+
+### Maintenance
+* Increment version to 2.15.0 ([#626](https://github.com/opensearch-project/job-scheduler/pull/626)).
+* dependabot: bump com.netflix.nebula.ospackage from 11.9.0 to 11.9.1 [(#634)](https://github.com/opensearch-project/job-scheduler/pull/634) [(#635)](https://github.com/opensearch-project/job-scheduler/pull/635).
+
+### Infrastructure
+* Refer to the version of Mockito from core's buildSrc/version.properties [(#630)](https://github.com/opensearch-project/job-scheduler/pull/630) [(#631)](https://github.com/opensearch-project/job-scheduler/pull/631).
+* Codecov GitHub Action changed back to v3 [(#622)](https://github.com/opensearch-project/job-scheduler/pull/622) [(#623)](https://github.com/opensearch-project/job-scheduler/pull/623).