Fix K3d dev script to better handle AWS sso

AWS SSO login creates a session using assumed roles, and this is a problem for the current K3d script, because the AWSUSERNAME varies with every session, creating new kube config files, security groups, and SSH keys. To avoid this, the script needs to be changed to pick the username set in the IdP, and in addition to that, it needs to take into account the fact that both IAM and AWS SSO logins might be used.