Configurable Custom Domain Support

1. Proposed title of this feature request:
Configurable Custom Domain

2. What is the nature and description of the request?
The Openshift Dedicated SRE team has received multiple requests to support a "Custom Domain" post-install ("Day-2 Operation"). A "Custom Domain" is a top-level domain that a customer manages (e.g. bmw.de). Customers want new Apps and the existing cluster services to be under this domain due to their own networking restrictions. Our solution for OSD v4 is to have a well known domain under openshiftapps.com that the customer can create a Wildcard CNAME to point to (e.g. _dns.apps.<cluster_name>.<shard>.<env>.openshiftapps.com).
We have identified all of the configurable items to modify for this to work (please see attached script). The problem is that this has been deemed unsafe as modifying the default cluster domain is unsupported and we have observed the native operators (such as the Authentication Operator) go degraded.

3. Why does the customer need this? (List the business requirements here)
Customers like BMW have private DNS server and many do not resolve to the default "openshiftapps.com" domain used by OSD during install. The customers also want to have a default domain (ingresses.config.openshift.io/cluster) when creating Apps without specifying a hostname during "oc expose".

4. List any affected packages or components.
cluster-ingress-operator, cloud-ingress-operator, authentication-operator