feature request: `gsutil ls` => sort by timestamp

As far as I can tell, `gsutil ls` (v5.25) does not allow for sorting by file/directory timestamps. I could use something like the following to accomplish this:

```bash
# List all files in a GCS bucket
files=$(gsutil ls gs://your-bucket-name/*)

# Initialize an empty associative array to hold file creation times
declare -A file_dates

# Loop through each file to get its creation date
for file in $files; do
creation_date=$(gsutil stat $file | grep "Creation time:" | awk -F: '{print $2 $3 $4}')
file_dates["$file"]=$creation_date
done

# Sort files by creation date and print
for file in $(echo "${!file_dates[@]}" | tr ' ' '\n' | sort -k3); do
echo "$file - ${file_dates[$file]}"
done
```

...but it would be great to have this feature built directly into `gsutil`

Start by examining the existing `gsutil ls` behavior and the `gsutil stat` output used in the issue's workaround. Define how timestamp sorting should be requested and ordered, then verify that `gsutil ls` can list files and directories sorted by their timestamps without the external shell loop.

Written by the indexing model from the issue text.