Please document 3scale-operator usage and the relation between 3scale and 3scale-operator.

I filed some Q & A in these KCS:

• What's the relation between 3scale versions and 3scale-operator versions?
• Does 3scale operator update 3scale automatically after the version is updated?
• How to update 3scale and 3scale-operator when "Operator ApprovalStrategy" is "Manual"
• Can users receive a notification when new container version is released on Container Catalog?
• Is it possible to downgrade operator versions?
• Is there any way to install older operator versions?
• Is it possible 3scale-operator upgrade requires manual operation?
• Can I edit DeploymentConfigs of 3scale directly?
• How to configure storage class of system-storage pvc on 3scale opeator
• How to configure storage class of system-mysql, system-redis and backend-redis pvc on 3scale operator
• 3scale Operator deletes user created secrets when APIManager is deleted

Unanswered questions:

• How to update 3scale when "Operator ApprovalStrategy" is "Manual"? Can users receive a notification new 3scale version is released?
• Is it possible 3scale-operator upgrade requires manual operation? For example, if a new 3scale operator requires an extra parameter, how to upgrade?
• Is there any way to install older operator versions?
• Is it possible to downgrade operator versions?
• Can I edit DeploymentConfigs directly?
• What events is the operator observing? e.g. a DeploymentConfig changed, a pod is down, etc.
• How to restart 3scale? When it is installed via template, it's documented in KCS.
• How to use a custom storage class when installing 3scale on top of OpenShift 4.x with operators documented in KCS