### 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
fieldMapping(
                b -> b.field("type", "dense_vector")
                    .field("dims", dims)
                    .field("index", true)
                    .field("similarity", similarity)
                    .field("element_type", "byte")
            )
        );
        byte[] vector = new byte[dims];
        for (int i = 0; i < dims; i++) {
            vector[i] = randomByte();
        }
        ParsedDocument doc1 = mapper.parse(source(b -> b.array("field", vector)));
        List<IndexableField> fields = doc1.rootDoc().getFields("field");
        assertEquals(1, fields.size());
        assertThat(fields.get(0), instanceOf(KnnByteVectorField.class));
        KnnByteVectorField vectorField = (KnnByteVectorField) fields.get(0);
        assertEquals(dims, vectorField.fieldType().vectorDimension());
        assertEquals(VectorEncoding.BYTE, vectorField.fieldType().vectorEncoding());
        assertEquals(similarity.function, vectorField.fieldType().vectorSimilarityFunction());
        assertArrayEquals("Parsed vector is not equal to original.", vector, vectorField.vectorValue());
    }
    @Override
    protected void assertFetchMany(MapperService mapperService, String field, Object value, String format, int count) throws IOException {
        assumeFalse("Dense vectors currently don't support multiple values in the same field", false);
    }
    /**
     * Dense vectors don't support doc values or string representation (for doc value parser/fetching).
     * We may eventually support that, but until then, we only verify that the parsing and fields fetching matches the provided value object
     */