Document required permissions to run basti init

[tibuntu]

Bug Description

Hi there, we recently reduced IAM permissions for our developers which led to the situation that they can not longer run basti init by themselves. Could you please document the required permissions?

Right now Basti isn't really pointing out which permissions are missing (Which it btw. does when running a cleanup):

Error setting up bastion. Can't create IAM role for bastion instance. Access denied by IAM.

Thanks!

Steps to Reproduce

Do not grant your AWS user full IAM permissions and try to run basti init