ui: ceph: show muted health checks as muted

A check that an operator muted in Ceph still showed up as a red error
here, which makes muting look like it did nothing. Show a faded bell
and say so in the tooltip. It uses the same grey as the icon for the
unknown state, so a muted row draws less attention.

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