### 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/vectors/DenseVectorFieldMapperTests.java
private final int dims = between(5, 1000);
        private final ElementType elementType = randomFrom(ElementType.BYTE, ElementType.FLOAT);
        private final boolean indexed = randomBoolean();
        private final boolean indexOptionsSet = indexed && randomBoolean();
        @Override
        public SyntheticSourceExample example(int maxValues) throws IOException {
            Object value = elementType == ElementType.BYTE
                ? randomList(dims, dims, ESTestCase::randomByte)