Allow this module to use a separate AWS key from s3fs key

Problem/Motivation

This module currently piggybacks credentials used in the s3fs module. For the site I'm working on, the keys used for s3fs and CloudFront are separate. We need to have a way to use a different key from the s3fs key.

Proposed resolution

• Use $settings['aws.access_key'] and $settings['aws.secret_key']
• Fallback to $settings['s3fs.access_key'] and $settings['s3fs.secret_key'] if above is not provided

Remaining tasks

Write a patch to use $settings['aws.access_key'] and $settings['aws.secret_key']
Update README to reflect the change