Switch to use the AWS region from `~/.aws/config` file instead of looking it at the `~/.aws/credentials` first.
The main reason for that, AWS CLI sets the region inside the `~/.aws/config` file and we need both `config` and `credentials` to follow the AWS CLI approach.
Linear task: [[ https://linear.app/comm/issue/ENG-559/removing-aws-region-from-constants | ENG-559 ]]