add documentation for using private registry

[pdabelf5]

Proposed changes

Add documentation for installing from the operator images (including kube-rbac-proxy) from a private container registry

Checklist

Before creating a PR, run through this checklist and mark each as complete.

• I have read the CONTRIBUTING doc
• I have added tests that prove my fix is effective or that my feature works
• I have checked that all unit tests pass after adding my changes
• I have updated necessary documentation
• I have rebased my branch onto main
• I will ensure my PR is targeting the main branch and pulling from my branch from my own fork

[jjngx]

👍🏻