osd/OSDMap: Show health warning if a pool is configured with size 1

osd/OSDMap: Show health warning if a pool is configured with size 1

Introduce a config option called 'mon_warn_on_pool_no_redundancy' that is
used to show a health warning if any pool in the ceph cluster is
configured with a size of 1. The user can mute/unmute the warning using
'ceph health mute/unmute POOL_NO_REDUNDANCY'.

Add standalone test to verify warning on setting pool size=1. Set the
associated warning to 'false' in ceph.conf.template under qa/tasks so
that existing tests do not break.

Fixes: https://tracker.ceph.com/issues/41666
Signed-off-by: Sridhar Seshasayee <sseshasa@redhat.com>