Add support for an Advertised Host other than PodIP when using Kubernetes cluster provider

[AdamCLarsen]

Description

This PR introduces an enhancement to the Kubernetes cluster provider to allow an advertised host to be added as a Pod label, when not using the PodIP. This feature for scenarios where the fully qualified domain name (FQDN) is needed, for example, when using TLS to secure the communications within the cluster. This change include logic to detected the pod subdomain, namespace, and cluster domain, to attempt to keep the hostname stored in the label under k8s's max length of 63 chars for Pod Label values.

When workloads of type Deployment are joining the Proto.Actor cluster, it is recommended to create a headless services definition, and to also add a spec.subdomain to the Pod definition that matches the name of the assigned headless service. See examples/ClusterK8sGrains for a working example.

Purpose

This pull request is a:

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist

• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)