api: ceph: add endpoints to mute and unmute health checks

Ceph can mute a health check. A muted check is still evaluated and
reported, but it no longer counts towards the overall cluster status.
For a check that an administrator cannot act on, muting is the only
option Ceph offers, and the cephx cipher checks in 19.2.6 and 20.2.4
are exactly that on a cluster whose kernel clients cannot use the new
cipher yet.

Muting was only possible from the command line, while the web
interface already marked muted checks as such. The endpoints expose
both an expiry and the sticky flag instead of picking one, because
which of them fits depends on why the check cannot be acted on.

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