[SQLint] add lint rule always using AS to rename columns

Good:
```sql
SELECT
  employees.name AS employee_name,
  COUNT(tasks.id) AS assigned_task_count
FROM
  employees LEFT JOIN tasks
    ON employees.id = tasks.id
```

Bad:
```sql
SELECT
  employees.name employee_name,
  COUNT(tasks.id) assigned_task_count
FROM
  employees LEFT JOIN tasks
    ON employees.id = tasks.id
```