Upgrade blackbox exporter, add ICMP probing support

Upgrade the blackbox exporter to the latest version (no notable changes in the upstream changelog from 0.23.0 to 0.25.0)

Add an icmp probing setup (needs the NET_RAW capability, see https://artifacthub.io/packages/helm/prometheus-community/prometheus-blackbox-exporter#to-7-0-0)