### 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
client().prepareIndex("index1").setId("2").setSource("field3", "value3", "new_field4", 100).get();
        }
        {
            
            assertAcked(indicesAdmin().preparePutMapping("index1").setSource("""
                    {
                      "runtime": {
                        "my_object.rfield1": null,
                        "rfield2" : null
                      }
                    }
                """, XContentType.JSON));
            
            client().prepareIndex("index1")
                .setId("1")
                .setSource("field3", "value3", "my_object2", Map.of("new_field1", "value1", "new_field2", "value2"));
        }
    }
    public void testMappingVersionAfterDynamicMappingUpdate() throws Exception {
        createIndex("test");
        final ClusterService clusterService = internalCluster().clusterService();
        final long previousVersion = clusterService.state().metadata().index("test").getMappingVersion();
        client().prepareIndex("test").setId("1").setSource("field", "text").get();
        assertBusy(() -> assertThat(clusterService.state().metadata().index("test").getMappingVersion(), equalTo(1 + previousVersion)));
    }
    public void testBulkRequestWithDynamicTemplates() throws Exception {
        final XContentBuilder mappings = XContentFactory.jsonBuilder();
        mappings.startObject();
        {