Add support for "APIcast 3scale managed" option for Product CR while still allowing custom staging/prod gateway URLs

[dlydiard]

using apicastSelfManaged does not automatically create Route resources which is not desired. Product should support using the "APIcast 3scale managed" product configuration, while still allowing customization of the staging/production gateway URLs and taking advantage of 3scale auto route creation.

[briangallagher]

JIRA to investigate: https://issues.redhat.com/browse/THREESCALE-10718