Add Custom Session Name Using Okta Username

[jonasoneves]

This change allows AWS session names to use the Okta username instead of the default botocore-session format, enhancing traceability and user identification in AWS logs.

By modifying _get_sts_creds to accept a session_name parameter and passing the Okta username as session_name from prepare_data, this update sets the AWS session name to the authenticated Okta username. This is especially useful for environments with multiple users, making it easier to track and identify session ownership across AWS services.