Upgrade Operator Gatekeeper API to v1alpha2

[font]

This tracks the changes that should be made when updating the operator's Gatekeeper API to v1alpha2.

• Remove the spec.image.image field and solely rely on the operator's RELATED_IMAGE_GATEKEEPER environment variable. There should be at least one release of the operator made that deprecates this spec.image.image field prior to this field being removed.
• Separate out common Gatekeeper options e.g. Affinity,NodeSelector, Tolerations, into the controller manager (WebhookConfig) and audit (AuditConfig) API options.
• Consider renaming WebhookConfig to ControllerConfig or something more meaningful.

[thomasmckay]

https://kubernetes.io/docs/tasks/extend-kubernetes/custom-resources/custom-resource-definition-versioning/