Proposed title of this feature request

Enable OLM when mirror registry is in a disconnected network (no internet connection)

What is the nature and description of the request?

The documentation on using OLM on restricted networks in OCP 4.5 does not cover the scenrio where the mirror registry is on a restricted network as the doc says 

 For this example, the procedure assumes use of a mirror registry that has access to both your network and the Internet.

Setting up the mirror registry doc does not explain how olm catalog build can be performed to enable OLM.

Hence, the RFE is to add a section to the docs that explains how to mirror the catalog and  operator images when the mirror registry has no access to the internet. 

Why does the customer need this? (List the business requirements here)

Customer has setup a totally disconnected install where the Mirror registry does not have internet access but want some operators to be installed from OperatorHub.