ublk: add feature UBLK_F_QUIESCE

Add feature UBLK_F_QUIESCE, which adds control command `UBLK_U_CMD_QUIESCE_DEV`
for quiescing device, then device state can become `UBLK_S_DEV_QUIESCED`
or `UBLK_S_DEV_FAIL_IO` finally from ublk_ch_release() with ublk server
cooperation.

This feature can help to support to upgrade ublk server application by
shutting down ublk server gracefully, meantime keep ublk block device
persistent during the upgrading period.

The feature is only available for UBLK_F_USER_RECOVERY.

Suggested-by: Yoav Cohen <yoav@nvidia.com>
Link: https://lore.kernel.org/linux-block/DM4PR12MB632807AB7CDCE77D1E5AB7D0A9B92@DM4PR12MB6328.namprd12.prod.outlook.com/


Signed-off-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20250522163523.406289-3-ming.lei@redhat.com


Signed-off-by: Jens Axboe <axboe@kernel.dk>