Allow AWS securityGroupOverrides

[ethanchowell]

In our environment, we're not allowed to create new security groups which essentially forces us into the UPI model even though we have permissions to do everything else the installer needs. Using the UPI model makes things difficult because we then have to break apart the documented cloudformation to separate out actions based on IAM roles we have to assume.

I've been able to generate the capi manifests from the installer and patch those to get a working deployment using the securityGroupOverrides, but being able to handle this purely through the install-config would significantly simplify things and make OpenShift a more viable solution for our environments.