Test "CompletePreservationTask"

[djjuhasz]

Fixes #907

• Add an UpdatePreservationTask() to the persistence service and ent client,
• Use the persistence.UpdatePreservationTask() to update the db in package_.CompletePreservationTask() and allow unit testing
• Add unit tests for package_.CompletePreservationTask()

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 72.22222% with 15 lines in your changes are missing coverage. Please review.

Project coverage is 48.77%. Comparing base (e67eff0) to head (8057037). Report is 1 commits behind head on main.

Files	Patch %	Lines
internal/persistence/telemetry.go	0.00%	9 Missing :warning:
...ternal/persistence/ent/client/preservation_task.go	79.31%	3 Missing and 3 partials :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #910 +/- ## ========================================== + Coverage 48.04% 48.77% +0.72% ========================================== Files 103 103 Lines 5561 5573 +12 ========================================== + Hits 2672 2718 +46 + Misses 2644 2609 -35 - Partials 245 246 +1 ```

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