Add "Note: OCP 4.x supports deployment of 3scale using the operator only. " here

Currently, it's only in section 2.6 but users make the decision to pick either deployment method right here, at the top of the page, and we should tell them right away that the only supported way to deploy on 4.x is via operators

Reported by: akaris

https://access.redhat.com/documentation/en-us/red_hat_3scale_api_management/2.7/html/installing_3scale/install-threescale-on-openshift-guide#annotations:c31bca09-0ff5-4b93-9172-5368c5f74e59