### Description

Dynamic mappings can greatly help the getting started experience but they currently don't apply to all types, one example is `dense_vector`.

It's been suggested to automatically map float arrays as dense vectors when there are more than 100 values, or a heuristic along these lines.
server/src/main/java/org/elasticsearch/index/mapper/DocumentParser.java
for (Mapper mapper : context.getDynamicMappers()) {
            rootBuilder.addDynamic(mapper.name(), null, mapper, context);
        }
        for (RuntimeField runtimeField : context.getDynamicRuntimeFields()) {
            rootBuilder.addRuntimeField(runtimeField);
        }
        RootObjectMapper root = rootBuilder.build(MapperBuilderContext.root(context.mappingLookup().isSourceSynthetic()));
        return context.mappingLookup().getMapping().mappingUpdate(root);
    }
    static void parseObjectOrNested(DocumentParserContext context) throws IOException {
        if (context.parent().isEnabled() == false) {
            context.parser().skipChildren();
            return;
        }
        XContentParser parser = context.parser();
        XContentParser.Token token = parser.currentToken();
        if (token == XContentParser.Token.VALUE_NULL) {
            
            return;
        }
        String currentFieldName = parser.currentName();
        if (token.isValue()) {
            throwOnConcreteValue(context.parent(), currentFieldName, context);
        }
        if (context.parent().isNested()) {
            context = context.createNestedContext((NestedObjectMapper) context.parent());
        }
        
        if (token == XContentParser.Token.END_OBJECT) {
            token = parser.nextToken();