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/000154_dbcrypt_key_ids.down.sql

@@ -1,5 +1,3 @@
-BEGIN;
-
 -- Before dropping this table, we need to check if there exist any
 -- foreign key references to it. We do this by checking the following:
 -- user_links.oauth_access_token_key_id
@@ -39,5 +37,3 @@ ALTER TABLE user_links
 
 -- Finally, drop the table.
 DROP TABLE IF EXISTS dbcrypt_keys;
-
-COMMIT;