Add `certmgr-stage` provisioner task
Following the line of missing functionality that ai-bs
does for us, we should implement a provisioner for certmgr-stage
call to open the window to request the certificate.
As this window is something only required at creation time, we should implement this logic as a provisioner and not as a normal resource as otherwise the window would be created at any run.
However, according to this it's not recommended to extend Terraform with third party provisioners. We should evaluate what's the more convenient approach.