[Feature] least and greatest function enhanced

[vkingnew]

function least and greateast default operation nulls value ，whether operate nulls value should up
to user .
-- current
select least(1,2,3,NULL) little,greatest(1,2,3,null) big;

-- expect：

-- desired feature：
least(col1,col2 [ignore|respect] nulls)
greatest(col1,col2 [ignore|respect] nulls)

-- statement example
select least(1,2,3,null ignore nulls) little,greatest(1,2,3,null,IGNORE nulls ) big;
select least(1,2,3,null,respect ignore nulls) little,greatest(1,2,3,null,respect nulls ) big;

[venkateshdatta1993]

@wangsimo0 I am new to this project and I'd like to give this a try.

Could you please assign this to me?

If there any pointers around approach to take or to start on this, please do share your thoughts.

Appreciate your support on this one :)