VPC: Add private subnet tag for alb

[GrigorovskyA]

Regarding: https://aws.amazon.com/ru/premiumsupport/knowledge-center/eks-vpc-subnet-discovery/

AWS LoadBalancer Controller requires "kubernetes.io/role/internal-elb" tag on a private subnet

[akastav]

Key: kubernetes.io/role/internal-elb
Value: 1
This tag is required if you want to use not all networks, only those that have this tag. It is necessary only if your architecture includes dedicating instances for ingress or some specific case. By default, we don't need to add this, but a good point to get the ability to set this if required. Maybe add some variables for this?

[trolleksii]

@akastav
Apparently this tag affects AWS LB Controller subnet discovery, and it is described both in AWS docs and the AWS LB Controller docs.
We are struggling now with internal facing ingresses not being able to detect usable subnet.

There is a similar tag in the code but the word ordering is confused:

  private_subnet_tags = {
    Name                                        = "${var.environment}-${var.cluster_name}-private"
    "kubernetes.io/role/elb-internal"           = "1"
    "kubernetes.io/cluster/${var.cluster_name}" = "owned"
  }

while it should be kubernetes.io/role/internal-elb. The value itself doesn't seem to make any difference, either "" or "1" should work the same.