[FEATURE]: integrate with pgroll for migrations

### Describe what you want

[`pgroll`](https://github.com/xataio/pgroll) is a tool that:
> * Zero-downtime migrations (no database locking, no breaking changes).
> * Keep old and new schema versions working simultaneously.
> * Automatic columns backfilling when needed.
> * Instant rollback in case of issues during migration.
> * Works against existing schemas, no need to start from scratch.

I think their JSON "Operations" is a bespoke set and I couldn't find any easy/obvious way to create it: https://github.com/xataio/pgroll/blob/main/docs/README.md#operations-reference

Seems like a match made in heaven if drizzle could generate the change spec similar to the existing migrations feature.