Support using profile-based credentials for S3 binary storage

Instead of relying on the username/password configuration stored in ModeShape configuration file, it would be useful to support credentials available in the (default) AWS profile (i.e. ~/.aws/credentials on Unix).

This behavior could be triggered when both the username and password are not provided in the ModeShape configuration.

Question: should a "profile-name" parameter be then supported as well, to be able to choose the AWS profile to use?