dashboards release v4.18.0

Fixed

• Fix memory usage calculation in nodes-overview and cluster-overview dashboards by using node_memory_MemAvailable_bytes instead of node_memory_MemFree_bytes, which incorrectly excluded cached/buffered memory from free memory

Changed

• Update DNS dashboard
  • Add new node and pod filters
  • Update variables description and query to use coredns_build_info as label source
  • Remove cache prefetch panel since the metric is gone
  • Fix DNS dashboard log panels
• Kube-Builder Operators dashboard: add a logs datasource selector