array_modify: Change default value of length?

[m-mohr]

[...] I think a default length=1 is unnecessarily opinionated.

I would propose to use 0 by default, or not having a default at all

Originally posted by @soxofaan in #309 (comment)

[m-mohr]

[...] I couldn't find a less opinionated alternative yet assuming that the main use cases are "update" and "remove" as we also have array_append and array_concat for common insert use cases.
I don't feel like there are a lot of common use cases for inserting in-between elements, but length = 0 would mostly cater for them.
Length = null (i.e. length of values) would only really cater to the update use case and seems to make descriptions more complex. None of the examples would get less complicated, instead, we need to add the length to all of them.

Answer from #309 by @soxofaan :

I don't think that the existence of array_append and array_concat is a reason to arbitrary pick default length=1.

One could argue that default length=0 is also opinionated, but at least it is the least destructive option (any length>0 removes data)

Another defense for in favor for the length=0 default is that the most obvious default array is an empty array (length 0).

[m-mohr]

Change to length = 0