Add release notes for 2.19.0 (#1412)

* Add release notes for 2.19.0

Signed-off-by: Owais <owaiskazi19@gmail.com>

* Addressed PR comments

Signed-off-by: Owais <owaiskazi19@gmail.com>

---------

Signed-off-by: Owais <owaiskazi19@gmail.com>
(cherry picked from commit ff200b2)
Signed-off-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>

Author: github-actions[bot]

release-notes/opensearch-anomaly-detection.release-notes-2.19.0.0.md

@@ -0,0 +1,23 @@
+## Version 2.19.0.0 Release Notes
+
+Compatible with OpenSearch 2.19.0
+
+### Features
+* Allow triggering anomaly only on drop or rise of features ([#1358](https://github.com/opensearch-project/anomaly-detection/pull/1358))
+* Add flattens custom result index when enabled ([#1401](https://github.com/opensearch-project/anomaly-detection/pull/1401)), ([#1409](https://github.com/opensearch-project/anomaly-detection/pull/1409))
+
+### Enhancements
+* Changing replica count to up 2 for custom result index ([#1362](https://github.com/opensearch-project/anomaly-detection/pull/1362))
+
+### Bug Fixes
+* Not blocking detector creation on unknown feature validation error ([#1366](https://github.com/opensearch-project/anomaly-detection/pull/1366))
+* Fix exceptions in IntervalCalculation and ResultIndexingHandler ([#1379](https://github.com/opensearch-project/anomaly-detection/pull/1379))
+
+### Infrastructure
+* Bump codecov/codecov-action from 4 to 5 ([#1369](https://github.com/opensearch-project/anomaly-detection/pull/1369))
+* Bump com.google.code.gson:gson from 2.8.9 to 2.11.0 ([#1375](https://github.com/opensearch-project/anomaly-detection/pull/1375))
+* Bump jackson from 2.18.0 to 2.18.2 ([#1376](https://github.com/opensearch-project/anomaly-detection/pull/1376))
+* Bump org.apache.commons:commons-lang3 from 3.13.0 to 3.17.0 ([#1377](https://github.com/opensearch-project/anomaly-detection/pull/1377))
+* Bump org.objenesis:objenesis from 3.3 to 3.4 ([#1393](https://github.com/opensearch-project/anomaly-detection/pull/1393))
+* Updating several dependencies ([#1368](https://github.com/opensearch-project/anomaly-detection/pull/1368))
+* Update recency_emphasis to be greater than 1 in test cases ([#1406](https://github.com/opensearch-project/anomaly-detection/pull/1406))