Limits asynchronous processing of single Backup/Restore task, aggregated by RequestedBackupAction or ScheduledBackup.
Background:
There are multiple controllers running in parallel. Locking mechanism is making sure that single RequestedBackupAction or ScheduledBackup is processed
only by one controller at a time.
Asynchronous processing:
Still all controllers are asynchronous - multiple RequestedBackupAction or ScheduledBackup of different .metadata.name are processed in parallel.
Reason:
Avoid loop - one controller is updating .status field of our CRD, another one receives an update and starts processing, but the first controller still not finished processing,
and then triggers a next .status update, and other controller is picking an update event... that's crazy! That's why we limit the parallelism, to make it simpler.