[/v4] - Add support for grouped migrations (prefactor)

[mfridman]

Added a helper function that takes a list of migrations and groups them by whether they are safe to run in a tx or not.

By grouping the migrations we can best effort apply them within the same transaction. See tests or this #485 (comment)

Description:

// GroupedMigrations enables the ability to share a single transaction across multiple migrations.
//
// For more information, see: TODO(mf): add link to docs
//
// For example, say we have 6 new migrations to apply: 11,12,13,14,15,16. But migration 14 is marked
// with -- +goose NO TRANSACTION. Then the migrations will be applied sequentially in 3 groups:
//
//  1. migrations 11,12,13 will be applied in a single transaction and committed
//  2. migration 14 will be applied outside transaction and committed
//  3. migrations 15,16 will be applied in a single transaction and committed
//
// This feature is useful to avoid leaving the database in a partially migrated state. But, keep in
// mind there may be performance implications if you have a large number of migrations.
//
// Default: false