### 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
.startObject("subfield")
                    .field("type", "keyword")
                    .endObject()
                    .endObject()
                    .endObject()
            )
        );
        ParsedDocument doc = defaultMapper.parse(source(b -> {
            b.startArray("objects");
            b.startObject().field("subfield", "sub").field("unmapped", "unmapped").endObject();
            b.endArray();
            b.startArray("unmapped");
            b.startObject().field("subfield", "unmapped").endObject();
            b.endArray();
        }));
        assertThat(doc.rootDoc().getFields("objects.subfield"), hasSize(1));
        assertThat(doc.rootDoc().getFields("objects.unmapped"), empty());
        assertThat(doc.rootDoc().getFields("unmapped.subfield"), empty());
        assertNull(doc.dynamicMappingsUpdate());
    }
    public void testArraysOfObjectsDynamicFalse() throws IOException {
        DocumentMapper defaultMapper = createDocumentMapper(
            dynamicMapping(
                "true",
                b -> b.startObject("objects")
                    .field("dynamic", false)
                    .startObject("properties")
                    .startObject("subfield")
                    .field("type", "keyword")
                    .endObject()