* Properly tag instances and subnets with `kubernetes.io/cluster/$cluster_name`

This is required by kubernetes to support multiple clusters in a single vpc/az

* Get rid of loadbalancer_apiserver_address as it is no longer needed

Rewrote AWS Terraform deployment for AWS Kargo. It supports now
multiple Availability Zones, AWS Loadbalancer for Kubernetes API,
Bastion Host, ...

For more information see README