modify schema primary keys to be nullable+defaulted

This fixes SQLAlchemy warnings related to primary keys not
having an auto_increment or nullable.

We've done this by making all foreign primary keys nullable.

In ApiRateLimit's case, we can set a default str to act as
a null, which seems a bit more sensible.

Signed-off-by: Kevin Morris <kevr@0cost.org>
1 job for pu_pk_nullable_defaults in 2 minutes and 50 seconds (queued for 2 seconds)