[GA] Allow customer managed DNS solutions for GCP: Implementation

Goal:

As an administrator, I would like to use my own managed DNS solution instead of only specific openshift-install supported DNS services (such as AWS Route53, Google Cloud DNS, etc...) for my OpenShift deployment.

Problem:

While cloud-based DNS services provide convenient hostname management, there's a number of regulatory (ITAR) and operational constraints customers face prohibiting the use of those DNS hosting services on public cloud providers.

Why is this important:

• Provides customers with the flexibility to leverage their own custom managed ingress DNS solutions already in use within their organizations.
• Required for regions like AWS GovCloud in which many customers may not be able to use the Route53 service (only for commercial customers) for both internal or ingress DNS.
• OpenShift managed internal DNS solution ensures cluster operation and nothing breaks during updates.

Dependencies (internal and external):

• DNS work for KNI
• https://docs.google.com/document/d/1VsukDGafynKJoQV8Au-dvtmCfTjPd3X9Dn7zltPs8Cc/edit

• This is a prerequisite for the internal clusters epic:   https://docs.google.com/document/d/1gxtIW6OlasVQtQLTyOl6f9H9CMuxiDNM5hQFNd3xubE/edit#

Prioritized epics + deliverables (in scope / not in scope):

• Ability to bootstrap cluster without an OpenShift managed internal DNS service running yet
• Scalable, cluster (internal) DNS solution that's not dependent on the operation of the control plane (in case it goes down)
• Ability to automatically propagate DNS record updates to all nodes running the DNS service within the cluster
• Option for connecting cluster to customers ingress DNS solution already in place within their organization

Estimate (XS, S, M, L, XL, XXL):

Previous Work:

Open questions:

Link to Epic: https://docs.google.com/document/d/1OBrfC4x81PHhpPrC5SEjixzg4eBnnxCZDr-5h3yF2QI/edit?usp=sharing