qa/tasks/cephadm: enable mon_cluster_log_to_file

qa/tasks/cephadm: enable mon_cluster_log_to_file

Without cluster_log_to_file we have nothing to grep for errors:

2023-10-27T16:06:59.111 DEBUG:teuthology.orchestra.run.smithi150:> sudo egrep '\[ERR\]|\[WRN\]|\[SEC\]' /var/log/ceph/38cc7fce-74d9-11ee-8db9-212e2dc638e7/ceph.log | egrep -v '\(MDS_ALL_DOWN\)' | egrep -v '\(MDS_UP_LESS_THAN_MAX\)' | head -n 1
2023-10-27T16:06:59.141 INFO:teuthology.orchestra.run.smithi150.stderr:grep: /var/log/ceph/38cc7fce-74d9-11ee-8db9-212e2dc638e7/ceph.log: No such file or directory

Set mon_cluster_log_to_file = true.

Fixes: https://tracker.ceph.com/issues/63425
Signed-off-by: Dan van der Ster <dan.vanderster@clyso.com>