[IBCDPE-935] private worker pool module

[BryanFauble]

Problem:

1. I wanted to take a little time and explore this enterprise feature while we had trial access. Private workers allow us to use drift detection for spacelift stacks.

Solution:

1. I created a terraform module for us to use that deploys private workers to a k8s cluster. I added notes in the readme about it as well so we can pick it up again in the future if we want to use this feature.

Testing:

1. I was able to deploy the private workers and turn on drift detection. See #dpe-topics slack channel.

[thomasyu888]

🔥 LGTM! Just a small comment in the code

[thomasyu888]

If we don't have the premium policy , does this work?

[BryanFauble]

Defining policies in this file just makes them available to be used. It does not add it to any stacks.

If this policy were added to a stack it would always pass because of the condition in .rego file:
input.spacelift.run.drift_detection

drift_detection would always not exist or be false in all cases.

Since I had already written this I was just going to leave it in.