### 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/DocumentParserContext.java
/**
     * Find a dynamic mapping template for the given field and its matching type
     *
     * @param fieldName the name of the field
     * @param matchType the expecting matchType of the field
     * @return the matching template; otherwise returns null
     * @throws DocumentParsingException if the given field has a dynamic template name specified, but no template matches that name.
     */
    public final DynamicTemplate findDynamicTemplate(String fieldName, DynamicTemplate.XContentFieldType matchType) {
        final String pathAsString = path().pathAsText(fieldName);
        final String matchTemplateName = sourceToParse().dynamicTemplates().get(pathAsString);
        for (DynamicTemplate template : root().dynamicTemplates()) {
            if (template.match(matchTemplateName, pathAsString, fieldName, matchType)) {
                return template;
            }
        }
        if (matchTemplateName != null) {
            throw new DocumentParsingException(
                parser().getTokenLocation(),
                "Can't find dynamic template for dynamic template name [" + matchTemplateName + "] of field [" + pathAsString + "]"
            );
        }
        return null;
    }
    
    
    private static class CopyToParser extends FilterXContentParserWrapper {
        enum State {
            FIELD,
            VALUE