terraform: collect apiserver cert SANs and support custom endpoint
constants: add new constants for cluster configuration and custom endpoint
cloud: support apiserver cert sans and prepare for endpoint migration on AWS
config: add customEndpoint field
bootstrapper: use per-CSP apiserver cert SANs
cli: route customEndpoint to terraform and add migration for apiserver cert SANs
bootstrapper: change interface of GetLoadBalancerEndpoint to return host and port separately
