This makes sure we don't need any workarounds for running Invidious with a local
PostgreSQL database.
Changing the default user should be fine as the new init script for PostgreSQL automatically
creates the new user and changes the existing database's owner to the new user. The old user
will still linger and must be removed manually.
See also: https://github.com/NixOS/nixpkgs/pull/266270
Invidious uses a strange setup where the database name is different from the system username
for non-explicit reasons.
Because of that, it makes it hard to migrate it to use `ensureDBOwnership`, we leave it to Invidious' maintainers
to pick up the pieces.
