Create shell prompt information about current session tool session

[bjornrog]

When using session tool it would be very helpful if the shell prompt could be altered to show information about current session. Like what profile you are currently using, if the session is with the bastion account or with an assumed role, and possibly also expiration status.

The use of such modifications to the prompt should be optional and default to off. To avoid intrusive changes to peoples existing prompt modifications. One possible way of handling that would be an aws configuration setting.