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/000035_linked_user_id.up.sql

@@ -1,5 +1,3 @@
-BEGIN;
-
 CREATE TABLE IF NOT EXISTS user_links (
 	user_id uuid NOT NULL,
 	login_type login_type NOT NULL,
@@ -70,5 +68,3 @@ FROM
 	user_links
 WHERE
 	user_links.user_id = users.id;
-
-COMMIT;