Make it possible to schedule orphan cleanup periodically as a task

[simenon]

Is your feature request related to a problem? Please describe.
kinda related to issue #6099 i opened, by misreading the docs. But in the end i want to schedule periodically an orphan cleanup

Describe the solution you'd like
Allow the orphan cleanup to be scheduled as a task from within pulp.

Describe alternatives you've considered
I could just schedule a cronjob from anywahere to call the orphan cleanup, but it feels to me that this just should be an option from within pulp.

Additional context
none