### 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/test/java/org/elasticsearch/index/mapper/DynamicMappingTests.java
public void testDynamicRuntimeLeafFields() throws IOException {
        DocumentMapper documentMapper = createDocumentMapper(dynamicMapping("runtime", builder -> {}));
        ParsedDocument doc = documentMapper.parse(source(b -> {
            b.field("long", 123);
            b.field("double", 123.456);
            b.field("string", "text");
            b.field("boolean", true);
            b.field("date", "2020-12-15");
        }));
        assertEquals(XContentHelper.stripWhitespace("""
            {
              "_doc": {
                "dynamic": "runtime",
                "runtime": {
                  "boolean": {
                    "type": "boolean"
                  },
                  "date": {
                    "type": "date"
                  },
                  "double": {
                    "type": "double"
                  },
                  "long": {
                    "type": "long"
                  },
                  "string": {
                    "type": "keyword"
                  }
                }