osd: Reduce default max backfill/recoveries for mclock to realistic limits

osd: Reduce default max backfill/recoveries for mclock to realistic limits

The earlier max number of backfill and recovery limits were overly
optimistic and caused recovery ops to overwhelm client ops regardless of
the mclock profile type.

Set the max backfill limit to 10. Set the max recovery limit to 10 for
osds having HDD backing device. For osds having SSD backing device, set
the recovery limit to 20.

Introduce and new config option, 'osd_mclock_override_recovery_settings',
that when set (false by default) allows the modification of the max
backfill and recovery options with mclock scheduler enabled.

It is important to note that with 'osd_mclock_override_recovery_settings'
disabled, the config subsystem will still allow the changes made to the
recovery and backfill settings when using the cli commands as the level at
which the change is made is always greater than CONF_DEFAULT. To counter this,
the osd will forcibly revert the recovery and backfill limits to the mClock
defaults by removing the existing setting from the config store and raises a
cluster log warning indicating the revert. This should force the user to set
the 'osd_mclock_override_recovery_settings' option first and then make changes
to the recovery and backfill limits.

Fixes: https://tracker.ceph.com/issues/57529
Signed-off-by: Sridhar Seshasayee <sseshasa@redhat.com>