Use the DeclarativeHotplugVolumes featureflag

[SkalaNetworks]

Currently, the CSI-driver uses the "HotPlug" feature-flag in Kubevirt, but the newest way of handling hotplug is through DeclarativeHotplugVolumes

[awels]

Correct we are actively working on getting the featuregate to GA in KubeVirt, so we don't have to specify the feature gate anymore.