text: Title: After inserting a fixture, update the primary key sequences
  Body: After inserting a fixture:
  
  https://github.com/piccolo-orm/piccolo/blob/8ec9d10313c9ac44916f01e27c9ef58eb22ae0d9/piccolo/apps/fixtures/commands/load.py#L57-L62
  
  For each primary key column we should run something like:
  
  ```sql
  SELECT setval('my_table_id_seq', (SELECT MAX(id) FROM my_table));
  ```
  
  To make sure subsequent inserts don't fail due to unique constraint errors.
  