Support restricted network environments

[jgawor]

Update operator to support installation in restricted network environments. Specifically:

• switch from image tags to image digests
• add relatedImages metadata for additional images.

Additional details in

• https://docs.openshift.com/container-platform/4.3/operators/operator_sdk/osdk-generating-csvs.html#olm-enabling-operator-for-restricted-network_osdk-generating-csvs
• https://docs.openshift.com/container-platform/4.3/openshift_images/image-configuration.html#images-configuration-registry-mirror_image-configuration

[arthurdm]

Closing in favour of https://github.com/application-stacks/runtime-component-operator/issues/131, since the Runtime Component Operator will replace the Appsody Operator.