Wrap postgres up migrations into a single transaction (#887)

internal/db/schema/migrations/postgres/0/41_targets.up.sql

@@ -1,3 +1,5 @@
+begin;
+
 /*
                                    ┌─────────────────┐
 ┌─────────────────┐                │   target_tcp    │
@@ -33,8 +35,6 @@
 
 */
 
-begin;
-
 create table target (
   public_id wt_public_id primary key,
   scope_id wt_scope_id not null