Adds post migration file support

This functionality adds a argument to load a sql file
from disk, parse its contents into the same blocks as
other sql files, but these blocks are appended to each
migration just before passing wildcards.

This solves a problem where a replicated database might
need to have its tables owned by a specific user or
a publication needs refreshing, but we don't want to
write duplicate sql in each migration that doesn't handle
actually changing the schema.

Fix version