Replace bastion with Runner Manager
What does this MR do?
Replace bastion with Runner Manager
From @tmaczukin's conversation in Slack:
We should update the https://docs.gitlab.com/runner/configuration/runner_autoscale_aws/index.html documentation and finally remove the Bastion name, changing it to how we call it in all other cases: Runner Manager. AFAIR The word Bastion was taken from one of the customers who worked with us on creating this configuration and docs.