Add featuregated automation tests to exercise this functionality :

• test that import mode is set base don CV's desired Architecture
• test that if the image.config.openshift.io config spec has import mode Legacy, imagestreams that are created without specifying the import mode has them set to Legacy
• test that if the image.config.openshift.io config spec has import mode PreserveOriginal, imagestreams that are created without specifying the import mode has them set to PreserveOriginal

Once these tests run for a release, we will have enough confidence that this signal proves we can make the featuregate default.