change access modified for DerivedFieldSupportedTypes

Signed-off-by: Rishabh Maurya <rishabhmaurya05@gmail.com>

Author: rishabhmaurya

server/src/main/java/org/opensearch/index/mapper/DerivedFieldSupportedTypes.java

@@ -31,7 +31,7 @@
 import java.util.function.Function;
 import java.util.stream.Collectors;
 
-public enum DerivedFieldSupportedTypes {
+enum DerivedFieldSupportedTypes {
 
     BOOLEAN("boolean", (name, context) -> {
         BooleanFieldMapper.Builder builder = new BooleanFieldMapper.Builder(name);