Add COLD_START option to ease fresh deployments

There are a few places in our Terraform code where the infrastructure doesn't start up properly from scratch. Two examples: (1) the `user_map` for the `aws-auth` ConfigMap can't be set right away, for some reason (this is a bug in the EKS terraform module that should be reported, but hasn't yet); (2) JupyterHub does not start with `proxy.https.enabled` set to true from the start, due to the unavailability of the route 53 alias record at the time of creation. In both cases, there is a flag that could be set when cold-starting that could offer a convenient method to deal with modules that exhibit poor behavior when being created from scratch (i.e., not modified from an existing state). `infra` should be modified to allow for this flag. If done correctly, this fix will also lay the groundwork for improving other features, like passing flags to Terraform when one-off configurations need to be set.