### 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
assertAcked(indicesAdmin().prepareCreate("test").setMapping("""
            {
              "_doc": {
                "properties": {
                  "obj": {
                    "properties": {
                      "runtime": {
                        "type": "object",
                        "dynamic": "runtime"
                      }
                    }
                  }
                }
              }
            }""").get());
        List<IndexRequest> docs = new ArrayList<>();
        docs.add(new IndexRequest("test").source("obj.one", 1));
        docs.add(new IndexRequest("test").source("anything", "anything"));
        
        docs.add(new IndexRequest("test").source("obj.runtime.one.two", "test"));
        docs.add(new IndexRequest("test").source("obj.runtime.one", "one"));
        docs.add(new IndexRequest("test").source("""
            {"obj":{"runtime":{"one":{"two": 1}}}}""", XContentType.JSON));
        Collections.shuffle(docs, random());
        BulkRequest bulkRequest = new BulkRequest();
        for (IndexRequest doc : docs) {
            bulkRequest.add(doc);
        }
        bulkRequest.setRefreshPolicy(WriteRequest.RefreshPolicy.IMMEDIATE);
        BulkResponse bulkItemResponses = client().bulk(bulkRequest).actionGet();