[FEATURE]: Add ability to use CTEs with UNION queries

### Describe what you want

When peforming a union, I would like to be able to use the "with" clause to define a CTE. For example:

```ts
const usersSubQuery = db
.$with('sq')
.as(getUserSubsetQuery());

await db.with(usersSubQuery).union(getFriendsWithSpecialDogsQuery,getFriendsWithSpecialCatsQuery);
```