Add functionality to dump audit log into csv file
Add functionality to dump audit log into csv file

Added a sub-manager for audit based tasks.
The `dump` task outputs the audit-log data in `csv` format by reusing the
`csv_generator` from `sqlaudit.py`.
The `rotate_audit` task is available in the `audit` sub-manager as well as
in the main manager for backward compatibility.

This fixes #1120

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