### 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
.source("host.name", "localhost", "host.id", 111, "time", 100, "time.max", 1000);
        IndexResponse indexResponse = client().index(request).actionGet();
        assertEquals(RestStatus.CREATED, indexResponse.status());
        assertBusy(() -> {
            Map<String, Object> mappings = indicesAdmin().prepareGetMappings("test").get().mappings().get("test").sourceAsMap();
            @SuppressWarnings("unchecked")
            Map<String, Object> properties = (Map<String, Object>) mappings.get("properties");
            assertEquals(4, properties.size());
            assertNotNull(properties.get("host.name"));
            assertNotNull(properties.get("host.id"));
            assertNotNull(properties.get("time"));
            assertNotNull(properties.get("time.max"));
        });
    }
    @SuppressWarnings("unchecked")
    public void testSubobjectsFalse() throws Exception {
        assertAcked(indicesAdmin().prepareCreate("test").setMapping("""
            {
              "_doc": {
                "properties": {
                  "foo.metrics" : {
                    "subobjects" : false,
                    "properties" : {
                      "host.name": {
                        "type": "keyword"
                      }
                    }
                  }
                }
              }