Region selection for `trailscraper select`

Hi,

Thanks for this great library. What is the best way to set this up? I am running from an ec2 instance with an instance profile that has access to the cloudtrail api but seeing:

```
trailscraper select --use-cloudtrail-api \
--filter-assumed-role-arn my-assumed-role \
--from 'one hour ago' \
--to 'now'
...
(large python stacktrace trimmed)
botocore.exceptions.NoRegionError: You must specify a region.
```

It does not look like there is a `region` option with `trailscraper select --help`.

Thanks again.

Start with the `trailscraper select` command and its `--help` output, then trace the `--use-cloudtrail-api` path to where the AWS client is configured. Done means users can provide a region when selecting through CloudTrail API and the command no longer raises `NoRegionError` on an EC2 instance.

Written by the indexing model from the issue text.