[feature] could we have pure SQL migration without JS files?

## I'm submitting a...

- [ ] Bug report
- [x] Feature request
- [ ] Question

## Current behavior

Creating migration always creates a boilerplate JS file that is committed to source.
The problem is that it can be edited -> broken.

It would be helpful to have only SQL files that would be processed in a uniform way, with some option.

## Expected behavior

`--sql` option that would look for sql files instead of JS

## What is the motivation / use case for changing the behavior?

As per above