Description of problem:

Currently there is no way to provide a mirroring configuration to ICI through the imageDigestSources field. The only way to properly provide it is through extraManifests. We should either decide if the clusterInstace CR should support this field or add a note that it should be done through extraManifests in the siteconfig documentation. 

Version-Release number of selected component (if applicable):

How reproducible:

100%