Column Tetris Automatisation

Hello,

In postgresl order of columns does have an non negligeable impact on table size[1].
Table are in many cases dynamic, and new fields can appear in the database life.
I suspect re-ordering columns based on types would be an automatisable task would be feaseable such:

```
reorderTableWithTetrisAlgo(table)
return reordered_table
```

Moreover, most client code should not be dependent on column order. Then a TETRIS option
in VACUUM FULL would be usefull for many users.

```
VACUUM [ FULL ] [ FREEZE ] [ VERBOSE ] [TETRIS] [ table ]
```

Does that makes sens ?

Thanks,

[1] https://developing.enectiva.cz/2016/05/15/postgres-column-tetris/