Add metrics and alerts for basic connectivity between ceph nodes and cloudvirts, specifically:

• mons <-> osds (non jumbo frames, public interface only)
• osds <-> osds (jumbo frames, public and cluster interfaces)
• cloudvirts -> osds (non jumbo frames, public interface only) (will change to jumbos once T330075: [cloudvirt] Enable jumbo frames on cloud-hosts/cloud-private interfaces is there)

The alerts should not page, but just show up in alertmanager when:

• More than 4 pings from a node failed in a short period
• More than 4 pings to a node failed in a short period
• More than 10% of the pings in total failed in a short period
• More than 2 pings from a node failed continuously in a medium period
• More than 2 pings to a node failed continuously in a medium period
• More than 5% of the pings in total failed in a medium period