### 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/internalClusterTest/java/org/elasticsearch/index/mapper/DynamicMappingIT.java
import org.elasticsearch.action.support.WriteRequest;
import org.elasticsearch.cluster.ClusterState;
import org.elasticsearch.cluster.ClusterStateUpdateTask;
import org.elasticsearch.cluster.metadata.IndexMetadata;
import org.elasticsearch.cluster.metadata.MappingMetadata;
import org.elasticsearch.cluster.service.ClusterService;
import org.elasticsearch.common.Randomness;
import org.elasticsearch.common.Strings;
import org.elasticsearch.common.geo.GeoPoint;
import org.elasticsearch.common.settings.Settings;
import org.elasticsearch.core.TimeValue;
import org.elasticsearch.index.query.GeoBoundingBoxQueryBuilder;
import org.elasticsearch.index.query.MatchQueryBuilder;
import org.elasticsearch.plugins.Plugin;
import org.elasticsearch.rest.RestStatus;
import org.elasticsearch.test.ESIntegTestCase;
import org.elasticsearch.test.InternalSettingsPlugin;
import org.elasticsearch.xcontent.XContentBuilder;
import org.elasticsearch.xcontent.XContentFactory;
import org.elasticsearch.xcontent.XContentType;
import org.hamcrest.Matchers;
import java.io.IOException;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.List;
import java.util.Map;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.atomic.AtomicReference;
import static org.elasticsearch.index.mapper.MapperService.INDEX_MAPPING_NESTED_FIELDS_LIMIT_SETTING;