fix: expand necessary OpenSearch permissions for data prepper (#6649)

Signed-off-by: Jongmin Chung <chungjm0711@gmail.com>

Author: JongminChung

data-prepper-plugins/opensearch/opensearch_security.md

@@ -18,6 +18,8 @@ or by using user credential assigned with a role that has the below required per
 - `cluster_all`
 - `indices:admin/template/get`
 - `indices:admin/template/put`
+- `indices:admin/index_template/get`
+- `indices:admin/index_template/put`
 - `indices:data/write/bulk`
 - `indices:data/write/bulks`