Add COLD_START option to ease fresh deployments

[jpolchlo]

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.