mon/LogMonitor: Use generic cluster log level config

mon/LogMonitor: Use generic cluster log level config

We do not control the verbosity of the LogEntry
which is getting logged to stderr, graylog and
journald. This causes excessive flooding of logs
to /var/log, making a filesystem to fill up quickly.
Also we have different config variables namely
mon_cluster_log_file_level and mon_cluster_log_to_syslog_level
to control verbosity at cluster log file and
syslog level respectively. Add a generic cluster log
level config variable which controls cluster log
verbosity for all external entities.

Additionally, this patch addresses the regression of
`mon_cluster_log_file_level` option which doesn't take effect
because of code refactoring of LogMonitor::update_from_paxos
(commit : 7c84e06).

Fixes: https://tracker.ceph.com/issues/57061
Fixes: https://tracker.ceph.com/issues/57049
Signed-off-by: Prashant D <pdhange@redhat.com>