Document and test the migration from a script based installation to an Operatorhub subscription

We need to document and test the steps for migrating from a script based installation to an Operatorhub subscription during an upgrade process. 

As a user, that previously relied on the installation scripts, I would like to follow Red Hat's recommendation and use the Operatorhub installation for Fuse Online, without starting from scratch, but through upgrading from 7.8 (script based install) to 7.9 (OLM based install).