Create task to delete soft-deleted items after a fixed time period

[david-code]

Description

Currently many of our models are "soft-deleted". This means instead of the data being deleted from the database, there is a column "deleted_at" set to the deletion time, and the row is ignored in queries fetching data. However we would also like to actually delete these rows after a fixed time period, that is remove them from the database entirely.

This issue will be to set up

• a recurring task
• that deletes items that were soft-deleted more than a fixed time period ago (say one month)

Additional context