Expose an admin-visible control to scale the persistent instance

[HalosGhost]

For really large-scale tests, the persistent test controller instance needs to be quite large, but leaving it scaled up to that size can be very costly. It's already quite easy to redeploy via terraform to change the configuration of the persistent instance, but it would be incredibly handy if we could expose a tool to immediately redeploy the persistent instance at a given configuration level. While this would effectively be temporary (because the next terraform apply would override it), it would make it really user-friendly to scale the persistent instance up or down ad-hoc without much effort.

Note: I'm not sure how difficult this would be to achieve, or even how possible it is (clearly the test controller is capable of requesting machine changes to the AWS environment, but I'm not sure if it could make changes to (more or less) its own configuration).