Tiered table engine

Syntax options:

```
Tiered(
  'table1,table2,table3', # list of tables
  'dt', # watermark column
  'dt>=today()-1,dt between today()-30 and today()-1,dt<today()-30' # list of watermark expressions, that may contain functions like today()
)
```

```
Tiered(dt, table1, interval 0 days, table2, interval 3 days, table3, interval 100 days);
```

UNION ALL under the covers