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/000157_workspace_agent_script.down.sql

@@ -1,5 +1,3 @@
-BEGIN;
-
 ALTER TABLE workspace_agent_logs SET LOGGED;
 
 -- Revert the workspace_agents table to its former state
@@ -19,5 +17,3 @@ ALTER TABLE workspace_agent_logs DROP COLUMN log_source_id;
 -- Drop the newly created tables
 DROP TABLE workspace_agent_scripts;
 DROP TABLE workspace_agent_log_sources;
-
-COMMIT;