[Spike] Devfile Registry Operator as a replacement of che-devfile-registry

[ibuziuk]

Need to investigate Devfile Registry Operator as a replacement of the che-devfile-registry.

The Devfile Registry operator manages the lifecycle of the following custom resources:

• Devfile Registry
• Devfile Registries List
• Cluster Devfile Registries List

Objectives:

• che-operator does not install and manage 'che-devfile-registry' operand anymore, https://github.com/devfile/registry-operator is planned to be deprecated in the short run
• if there is no Devfile Registry Operator and CR we show only the Empy Workspace Getting Started sample which is part of the User Dashboard
• if there is a Devfile Registry Operator and dedicated CR on the cluster, che-operator discovers the Devfile Registry automatically and refer to it from the Eclipse Che CR
• On the Dashboard devfiles from the discovered reistry are shown in the Getting Started page

[ibuziuk]

Closing, for now, we are looking forward to having the essential fixes on the Devfile registry end:

• Not possible to deploy the devfile registry via CR on OpenShift 4.12 #1092
  OperatorHub
• Make Registry operator available on operatorhub.io and in Operator catalog devfile/api#1007
• Put devfile registry operator to OperatorHub devfile/api#410
  Devfile registry air gap/offline installation Devfile registry air gap/offline installation devfile/api#329