Add way for `AWSShellScript` to use other shells besides bash

[JadenSimon]

Is your feature request related to a problem? Please describe.

Users have been using the AWS Tools for Powershell task just to get AWS credentials in a Powershell environment

Describe the solution you'd like

At minimum, there should be a way to use Powershell instead of bash with AWS credentials already set. Users should not need hack around tasks to do the things they need to do in a secure way.

Describe alternatives you've considered

Add a separate task. This could still be done.