PodNetworkConnectivityCheck gatherer reads too much data into memory

The PNCC gatherer obtains the complete list of the "PodNetworkConnectivityCheck" resources in a cluster and marshals it into JSON. It seems there can be a lot of PNCC resources (in bigger clusters and especially when there's some network problem). The gatherer also doesn't filter the PNCC according the time, which means there can a year old PNCC failures in the archive.