ui: ceph: explain the cephx cipher health checks

Every cluster upgraded to Ceph 19.2.6 or newer reports the cephx keys
that are not migrated yet as insecure, two of them as errors. Six auth
errors with no explanation do not say that storage keeps working.

The explanation goes into the detail of the row. It only concerns
these checks, and above the grid it would stay on screen on every
upgraded cluster until the keys are migrated.

Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>