Optimise haystack updates on save

When saving a Person object, we see about 25 index update jobs being triggered in celery. This leads up to things like AlekSIS-App-LDAP#23 (closed).

We should find out what these jobs are, whether they are improperly debounced update jobs for the object itself, or maybe for related object or such, etc.

added part::backend type::bug workflow::confirmed labels

Closed by !485 (merged), de facto duplicate of #350 (closed).

closed