Always write doc_values param to mapping for wildcard field

I made a mistake making this parameter default to false. In 3.0,
I would like to switch the default to true. An index upgraded from
2.x with the default (false) value should specifically emit the
value to avoid implicitly picking up the new default (true).

Signed-off-by: Michael Froh <[email protected]>

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

@@ -101,7 +101,7 @@ public static final class Builder extends ParametrizedFieldMapper.Builder {
         );
         private final Parameter<String> normalizer = Parameter.stringParam("normalizer", false, m -> toType(m).normalizerName, "default");
         private final Parameter<Map<String, String>> meta = Parameter.metaParam();
-        private final Parameter<Boolean> hasDocValues = Parameter.docValuesParam(m -> toType(m).hasDocValues, false);
+        private final Parameter<Boolean> hasDocValues = Parameter.docValuesParam(m -> toType(m).hasDocValues, false).alwaysSerialize();
         private final IndexAnalyzers indexAnalyzers;
 
         public Builder(String name, IndexAnalyzers indexAnalyzers) {