Refactor protobuf by moving the nested enum outside the message and renaming the field following naming convention (opensearch-project#228)

Signed-off-by: lucy66hw <fridalu66@gmail.com>

Author: lucy66hw

CHANGELOG.md

@@ -6,6 +6,7 @@ Inspired from [Keep a Changelog](https://keepachangelog.com/en/1.0.0/)
 ### Added
 
 ### Changed
+-  Refactor protobuf by moving the nested enum outside the message and renaming the field following naming convention  ([#228](https://github.com/opensearch-project/opensearch-protobufs/pull/228))
 
 ### Removed