### 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/main/java/org/elasticsearch/index/mapper/vectors/DenseVectorFieldMapper.java
if (similarity == VectorSimilarity.COSINE && Math.sqrt(squaredMagnitude) == 0.0f) {
                        errorBuilder = new StringBuilder(
                            "The [" + similarity + "] similarity does not support vectors with zero magnitude."
                        );
                    }
                } else {
                    if ((similarity == VectorSimilarity.COSINE || similarity == VectorSimilarity.DOT_PRODUCT)
                        && Math.sqrt(squaredMagnitude) == 0.0f) {
                        errorBuilder = new StringBuilder(
                            "The [" + similarity + "] similarity does not support vectors with zero magnitude."
                        );
                    }
                }
                if (errorBuilder != null) {
                    throw new IllegalArgumentException(appender.apply(errorBuilder).toString());
                }
            }
            @Override
            public Field parseKnnVector(DocumentParserContext context, DenseVectorFieldMapper fieldMapper) throws IOException {
                int index = 0;
                float[] vector = new float[fieldMapper.dims];
                float squaredMagnitude = 0;
                for (Token token = context.parser().nextToken(); token != Token.END_ARRAY; token = context.parser().nextToken()) {
                    fieldMapper.checkDimensionExceeded(index, context);
                    ensureExpectedToken(Token.VALUE_NUMBER, token, context.parser());
                    float value = context.parser().floatValue(true);
                    vector[index++] = value;
                    squaredMagnitude += value * value;
                }
                fieldMapper.checkDimensionMatches(index, context);