CREATE AGGREGATE array_cat

Hi, I wonder why there's no function to aggregate arrays by
concatenation out of the box?

There is a usual function `array_cat(anyarray, anyarray)`, but it
doesn't seamlessly work with grouping.

Wouldn't it be natural to have this:

CREATE AGGREGATE array_cat (anyarray)
(
    sfunc = array_cat,
    stype = anyarray,
    initcond = '{}'
);

Thanks,
Vlad