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.up.sql

@@ -1,4 +1,3 @@
-BEGIN;
 CREATE TABLE workspace_agent_log_sources (
 	workspace_agent_id uuid NOT NULL REFERENCES workspace_agents(id) ON DELETE CASCADE,
 	id uuid NOT NULL,
@@ -33,4 +32,3 @@ ALTER TABLE workspace_agents DROP COLUMN startup_script;
 
 -- Set the table to unlogged to speed up the inserts
 ALTER TABLE workspace_agent_logs SET UNLOGGED;
-COMMIT;