feat: run all migrations in a transaction (#10966)

Updates coder/customers#365

This PR updates our migration framework to run all migrations in a single transaction. This is the same behavior we had in v1 and ensures that failed migrations don't bring the whole deployment down. If a migration fails now, it will automatically be rolled back to the previous version, allowing the deployment to continue functioning.

coderd/database/migrations/000148_group_source.down.sql

@@ -1,8 +1,4 @@
-BEGIN;
-
 ALTER TABLE groups
 	DROP COLUMN source;
 
 DROP TYPE group_source;
-
-COMMIT;