mds/MDSRank: Add set_history_slow_op_size_and_threshold for op_tracker

mds/MDSRank: Add set_history_slow_op_size_and_threshold for op_tracker

void OpHistory::_insert_delayed(const utime_t& now, TrackedOpRef op)
{
...
  double opduration = op->get_duration();
...
  if (opduration >= history_slow_op_threshold.load()) {
    slow_op.insert(make_pair(op->get_initiated(), op));
    logger->inc(l_trackedop_slow_op_count);
  }
...
}
mds op_tracker have no set slow op threshold, and history_slow_op_threshold default
value is 0, cause to mds have slow op alway.

Fixes: https://tracker.ceph.com/issues/61749
Signed-off-by: Yite Gu <yitegu0@gmail.com>