Update baseline maintainer and CODEOWNER format

Update baseline maintainer to include repo owners.
Update format to match other repos. Otherwise
it only add the last reviewer always.

Issue Resolve
opensearch-project#2878

Signed-off-by: Anan Zhuang <ananzh@amazon.com>

.github/CODEOWNERS

@@ -1,8 +1 @@
-@ariamarble
-@carolxob
-@cwillum
-@hdhalter
-@JeffH-AWS
-@kolchfa-aws
-@Naarcha-AWS
-@vagimeli
+*   @ariamarble @carolxob @cwillum @hdhalter @JeffH-AWS @kolchfa-aws @Naarcha-AWS @vagimeli @ananzh @seanneumann @AMoo-Miki

MAINTAINERS.md

@@ -14,4 +14,6 @@ This document contains a list of maintainers in this repo. See [opensearch-proje
 | Fanit Kolchina   | [kolchfa-aws](https://github.com/kolchfa-aws)   | Amazon      |
 | Nate Archer      | [Naarcha-AWS](https://github.com/Naarcha-AWS)   | Amazon      |
 | Melissa Vagi     | [vagimeli](https://github.com/vagimeli)         | Amazon      |
-
+| Anan Zhuang      | [ananzh](https://github.com/ananzh)             | Amazon      |
+| Sean Neumann     | [seanneumann](https://github.com/seanneumann)   | Amazon      |
+| Miki Barahmand   | [AMoo-Miki](https://github.com/AMoo-Miki)       | Amazon      |