dynamic_types example does not print the projection

[martin-g]

Describe the bug

https://github.com/apache/arrow-rs/blob/master/arrow/examples/dynamic_types.rs shows how to use and project RecordBatches.
I think it would be a slightly more useful if it actually prints the original and the projection.

To Reproduce

$ cd arrow
$ cargo run --example dynamic_types

Expected behavior

Print the RecordBatches, e.g.:

+----+-----+
| id | sum |
+----+-----+
| 1  | 2.2 |
| 2  | 3.3 |
| 3  | 4.4 |
| 4  | 5.5 |
| 5  | 6.6 |
+----+-----+

Additional context
N/A