Add RHOCS4 as an additional storage backend option to all Quay docs

Add RHOCS 4 to all product docs where we call out the list of supported storage options for Quay. 

In contrast to RHOCS3 via NooBaa which we started to support with Quay v3.1 but only as Tech Preview the RHOCS4 support including NooBaa will be marked as GA with the launch of RHOCS4. Currently targeted shortly after Quay 3.2 and OCP 4.3 comes out (Dec 11th). RHOCS3 support will remain marked as Tech Preview.

Means that our product docs focus should be RHOCS4 and NooBaa with an additional pointer to the kbase article Chris is currently working on to describe the RHOCS3 implementation (tech preview).  

etamir put together an early draft of the documentation here: https://docs.google.com/document/d/16c7rREEo7qHJF1Z24rCd-9C2ZIpaKXtrwGbiTibGCXk/edit# 

We should aim to finish the content before we get Quay 3.2 out but wait publishing the RHOCS4 section until RHOCS4 has been officially released (hopefully e/o the year but still after Quay 3.2 probably).