### 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
DenseVectorFieldType denseVectorFieldType = denseVectorFieldMapper.fieldType();
        assertTrue(denseVectorFieldType.isIndexed());
        assertEquals(VectorSimilarity.COSINE, denseVectorFieldType.getSimilarity());
    }
    public void testAddDocumentsToIndexBefore_V_7_5_0() throws Exception {
        IndexVersion indexVersion = IndexVersion.V_7_4_0;
        DocumentMapper mapper = createDocumentMapper(
            indexVersion,
            fieldMapping(b -> b.field("index", false).field("type", "dense_vector").field("dims", 3))
        );
        float[] validVector = { -12.1f, 100.7f, -4 };
        ParsedDocument doc1 = mapper.parse(source(b -> b.array("field", validVector)));
        List<IndexableField> fields = doc1.rootDoc().getFields("field");
        assertEquals(1, fields.size());
        assertThat(fields.get(0), instanceOf(BinaryDocValuesField.class));
        
        BytesRef vectorBR = fields.get(0).binaryValue();
        float[] decodedValues = decodeDenseVector(indexVersion, vectorBR);
        assertArrayEquals("Decoded dense vector values is not equal to the indexed one.", validVector, decodedValues, 0.001f);
    }
    private static float[] decodeDenseVector(IndexVersion indexVersion, BytesRef encodedVector) {
        int dimCount = VectorEncoderDecoder.denseVectorLength(indexVersion, encodedVector);
        float[] vector = new float[dimCount];
        VectorEncoderDecoder.decodeDenseVector(indexVersion, encodedVector, vector);
        return vector;
    }
    public void testDocumentsWithIncorrectDims() throws Exception {
        for (boolean index : Arrays.asList(false, true)) {
            int dims = 3;
            XContentBuilder fieldMapping = fieldMapping(b -> {