Create test setup for Azure DNS integration

[abaguas]

As stated in #1772, we would like to have test setup with the main DNS providers. This PR creates a complete guide documenting how to test the Azure integration, including terraform and helm configuration.

According to the docs the infrastructure should cost $0.90 per month, but it can also be destroyed and re-provisioned anytime:

First 25 hosted DNS zones	$0.50 per zone per month
First billion DNS queries/month	$0.40 per million

[abaguas]

If you have a suggestion of another folder where to place this content let me know

[ytsarev]

@abaguas that's a great setup, thank you so much for your work on it. However, I am hesitant to merge any more terraform code to the repo after BUSL changes. I tested the alternative setup with Crossplane please see https://github.com/ytsarev/k8gb/tree/azure-crossplane/dns-providers/azure/crossplane .
The rest of the guide was almost intact and I got to a successful external-dns test in #1762

If you are ok with this route, I can create Crossplane-based abstraction(s) that will handle the test setup.

In the long run, I also plan to refactor to Crossplane and deprecate the old https://github.com/k8gb-io/k8gb/tree/master/docs/examples/route53/terraform-aws-eks-k8gb reference architecture to fully eliminate the Terraform footprint in this repository.