Move service feedback Performance Platform stats upload from the 'support' app

The `support` app is being split into a frontend-only component and an API component (this app). Part of this work is moving the Performance Platform stats upload batch job.

This code has been lifted from the `support` app (it's functionally identical), and will be removed from the `support` app once this change is deployed.
I've added https://github.gds/gds/alphagov-deployment/pull/697 for this.