Specify up/down migrate functions with optional args

[wevre]

The up/down migration function entries in a code-based migration file can optionally be a vector syntax, e.g. {..., :up-fn [migrate-up "arg1" :arg2], ...}, where the additional args will be passed to the migration function after the config map.

[yogthos]

Thanks, looks good but I'm noticing a test is failing now. Actually, that looks unrelated to the pr. It's my local docker setup, so I think we're good.