Pass config to a setup or preflight function

[yhahn]

Many migration scripts are meant to target a very specific table and could lead to Bad Things :disappointed: if run on others.

I've currently hacked some sanity checks for the table being targeted (and bailing out) by inspecting process.argv from my migrate module but it would be cleaner/more reliable for a setup or preflight function to be called with these options (method/region/table might be sufficient?)

I can take a quick pass at implementing this if this sounds reasonable.

cc @rclark @emilymcafee

[rclark]

Sounds good. It could follow a similar pattern to how we handle optional finish scripts.