s3 ls --short

Currently the command `aws s3 ls --recursive mybucket` gives long-form results with timestamp, filesize, and key:
```
2021-11-04 14:29:56 3714945 sub/foo.csv
2021-11-19 22:58:25 3706448 bar.csv
2021-11-30 17:01:54 485 baz.csv
```

It would be nice to specify an option to show short-form results that give the key only, like
```
aws s3 ls --short --recursive mybucket
sub/foo.csv
bar.csv
baz.csv
```

without resorting to external commands to parse out the key, as described in these [answers on stackoverflow](https://stackoverflow.com/questions/36813327/how-to-display-only-files-from-aws-s3-ls-command)