Add Sarthak Aggarwal as a maintainer (#69) (#70)

(cherry picked from commit 613e058)

Signed-off-by: Andrew Ross <andrross@amazon.com>
Signed-off-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>
Co-authored-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>

Author: opensearch-trigger-bot[bot]

.github/CODEOWNERS

@@ -1 +1 @@
-*   @andrross @reta @nknize
+*   @andrross @reta @nknize @sarthakaggarwal97

MAINTAINERS.md

@@ -7,6 +7,7 @@ This document contains a list of maintainers in this repo. See [opensearch-proje
 | Andrew Ross      | [andrross](https://github.com/andrross)                   | Amazon      |
 | Andriy Redko     | [reta](https://github.com/reta)                           | Aiven       |
 | Nicholas Knize   | [nknize](https://github.com/nknize)                       | Amazon      |
+| Sarthak Aggarwal | [sarthakaggarwal97](sarthagg@amazon.com)                  | Amazon      |
 
 ## Emeritus