Provide the option to expose the registry through https

[pbochynski]

Description
Provide a way to expose the docker registry using TLS certificates. It can be an optional setting that utilizes istio/api-gateway features.

Reasons
Some customers use tools that enforce secure access to the registry with TLS.

Execution

• POC: manually expose docker registry via https using istio resources (document the steps in /docs/user )
• verify if docker CLI can be used against https exposed endpoint
• implement an "auto-pilot" mode : implement auto-exposure in docker registry operator