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.up.sql

@@ -1,5 +1,3 @@
-BEGIN;
-
 CREATE TYPE group_source AS ENUM (
     -- User created groups
 	'user',
@@ -11,5 +9,3 @@ ALTER TABLE groups
 	ADD COLUMN source group_source NOT NULL DEFAULT 'user';
 
 COMMENT ON COLUMN groups.source IS 'Source indicates how the group was created. It can be created by a user manually, or through some system process like OIDC group sync.';
-
-COMMIT;