Cleanup mechanisms for findings, engagements, tests and risk acceptances

[twwd]

Is your feature request related to a problem? Please describe

We use a very large DefectDojo instance with several hundred thousand findings per year. To keep the database small and the application performant, we need to get rid of old things.

Describe the solution you'd like

As a DefectDojo admin, I want to enable that

1. closed findings are automatically deleted after a configurable number of days (e.g., 365),
2. tests without finds are automatically deleted after a configurable number of days (e.g., 365),
3. engagements without tests are automatically deleted after a configurable number of days (e.g., 365),
4. risk acceptances without any linked findings are automatically deleted after a configurable number of days (e.g., 365).

Describe alternatives you've considered

Currently, we use an external script that is run scheduled that uses the API to perform these tasks.
This script is inefficient sind it is slow and creates a high database load. If we use to much threads for it, it kills our DefectDojo instance.