Adding new maintainers to ISM (#1321)

Signed-off-by: vikasvb90 <vikasvb@amazon.com>
(cherry picked from commit 6bdf7cb)
Signed-off-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>

.github/CODEOWNERS

@@ -1 +1 @@
-*   @bowenlan-amzn @Hailong-am @vikasvb90
+*   @bowenlan-amzn @Hailong-am @vikasvb90 @tandonks @shiv0408 @soosinha

MAINTAINERS.md

@@ -9,6 +9,9 @@ This document contains a list of maintainers in this repo. See [opensearch-proje
 | Vikas Bansal          | [vikasvb90](https://github.com/vikasvb90)             | Amazon      |
 | Bowen Lan             | [bowenlan-amzn](https://github.com/bowenlan-amzn)     | Amazon      |
 | Hailong Cui           | [Hailong-am](https://github.com/Hailong-am)           | Amazon      |
+| Kshitij Tandon | [tandonks](https://github.com/tandonks) | Amazon |
+| Shivansh Arora | [shiv0408](https://github.com/shiv0408) | Amazon |
+| Sooraj Sinha | [soosinha](https://github.com/soosinha) | Amazon |
 
 ## Emeritus