make router namespace ownership check configurable with MicroShift

Feature Overview (aka. Goal Summary)

OpenShift Default is not to allow multiple namespaces to access the same hostname. MicroShift inherits that default.  The goal of this feature is to give customers a choice and make this configurable. 

Goals (aka. expected user outcomes)

• Expose a configuration option to control the namespace ownership check in the router to allow multiple routes/ingress resources to use the same hostname but different paths.

Requirements (aka. Acceptance Criteria):

1. As a MicroShift admin, I want to configure MicroShift to support combining routes from multiple namespaces ("inter-namespace allowed").

Use Cases (Optional):

• Users who compose applications from multiple sources may deploy those to different namespaces, albeit want to expose them using the same hostname and different path. 

Out of Scope

n/a

Background

1. https://github.com/openshift/enhancements/blob/master/enhancements/ingress/openshift-route-admission-policy.md describes how the flag is exposed in OpenShift.
2. https://issues.redhat.com/browse/NE-243
3. https://github.com/openshift/api/blob/894b49f57a15cbce3869961e20cd9d52df6f8b0f/operator/v1/types_ingress.go#L918 

Customer Considerations

Requested by multiple EAP customers

Documentation Considerations

• Configuration option needs to be documented in the "configuring" book

Interoperability Considerations

None