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/000162_workspace_automatic_updates.up.sql

@@ -1,8 +1,6 @@
-BEGIN;
 -- making this an enum in case we want to later add other options, like 'if_compatible_vars'
 CREATE TYPE automatic_updates AS ENUM (
     'always',
     'never'
 );
 ALTER TABLE workspaces ADD COLUMN IF NOT EXISTS automatic_updates automatic_updates NOT NULL DEFAULT 'never'::automatic_updates;
-COMMIT;