Add support for XDG's AWS_CONFIG_FILE AWS_SHARED_CREDENTIALS_FILE

[pblgomez]

Feature Request

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

AWS support is limited to the configuration files being in ~/.aws and not following FreeDesktop.org XDG standard

Describe the solution you'd like

As described in https://docs.aws.amazon.com/cli/latest/userguide/cli-configure-files.html and in https://docs.aws.amazon.com/cli/latest/userguide/cli-configure-envvars.html those can be configured using $AWS_CONFIG_FILE and $AWS_SHARED_CREDENTIALS_FILE

Describe alternatives you've considered

It would be nice to be able to support AWS CLI environment variables before looking to the static ~/.aws directory.