Add toString() to CreateIndexRequest class.

Signed-off-by: Guillaume Alvarez <7364145+guillaume-alvarez@users.noreply.github.com>

server/src/main/java/org/opensearch/action/admin/indices/create/CreateIndexRequest.java

@@ -594,4 +594,16 @@ public void writeTo(StreamOutput out) throws IOException {
         }
         waitForActiveShards.writeTo(out);
     }
+
+    @Override
+    public String toString() {
+        return "CreateIndexRequest{" +
+            "cause='" + cause + '\'' +
+            ", index='" + index + '\'' +
+            ", settings=" + settings +
+            ", mappings='" + mappings + '\'' +
+            ", aliases=" + aliases +
+            ", waitForActiveShards=" + waitForActiveShards +
+            '}';
+    }
 }