Added a maintainers file (#523)

based on the maintainers list that CEHENKLE posted in the forums here: https://discuss.opendistrocommunity.dev/t/preparing-opensearch-and-opensearch-dashboards-for-release/5567 

Signed-off-by: Dawn M. Foster <[email protected]>

MAINTAINERS.md

@@ -0,0 +1,13 @@
+# OpenSearch Maintainers
+
+## Maintainers
+| Maintainer | GitHub ID | Affiliation |
+| --------------- | --------- | ----------- |
+| Abbas Hussain | [abbashus](https://github.com/abbashus) | Amazon |
+| Charlotte | [CEHENKLE](https://github.com/CEHENKLE) | Amazon |
+| Harold Wang | [harold-wang](https://github.com/harold-wang) | Amazon |
+| Himanshu Setia | [setiah](https://github.com/setiah) | Amazon |
+| Nick Knize | [nknize](https://github.com/nknize) | Amazon | 
+| Rabi Panda | [adnapibar](adnapibar) | Amazon |
+| Sarat Vemulapalli | [saratvemulapalli](https://github.com/saratvemulapalli) | Amazon |
+| Tianli Feng | [tlfeng](https://github.com/tlfeng) | Amazon |