Add parallel backup/restore support for long running jobs

[jzilak]

It would be nice to have support for parallel operations for backup and restore to support long running jobs like 24 hours or more.
Currently any backup or restore job block any other operations on backup archives. Currently I facing issue, where recovery job running 36 hours and block any backup operation on affected job, because db file is locked by other restore job. Problem is that we lost many backup windows not only for restoring VM, but also for all others VM backed up with same job.

[foggy]

Hi Josef, parallel tasks are actually there but take into account the max number of concurrent tasks configured for involved proxies/repositories, so this might be the reason. Also, keep in mind that the same files might be involved in several tasks and it is technically not possible to backup to the file currently used by restore operation, for example.