Maintenance release tracker epic. For each CNV maintenance release, the HCO version number must be updated. 

in the _attributes/common-attributes.adoc, update the HCOVersion

For example:
:VirtProductName: OpenShift Virtualization
:HCOVersion: 4.15.7 {where the value is the previous maintenance version}
:HCOVersion: 4.15.8 {where the version number is updated}

When we ship zstream maintenance releases, we update the HCO version number and merge the PR so that the documentation reflects the current HCO Version number anywhere in the documentation that the HCO version attribute is used.