Fix updated_at function

[kiwicopple]

Chore

Describe the chore

This PR introduces an set_updated_at function, but it wasn't namespaced so it gets installed on the public schema. We should fix this so that it gets run on the "stripe" schema

Additional context

It will be a bit dangerous to run drop function public.set_updated_at() because this could now be used by others. We should go back and edit this migration file (which is generally not a done thing) so that it doesn't affect new users. Then we should also add a new migration to alter function if exists public.set_updated_at() set schema "stripe";