We accidentally removed the code for maximum complexity in commit
c984e666f. As mentioned in the documentation:
> The main risk factor is multiple collections of resources being
> requested in the same query.
We reject these requests by limiting the complexity.
The `max_complexity` option depends on the page size being set. Without
it, we get an error:
```
Can't calculate complexity for User.public_debates, no `first:`,
`last:`, `max_page_size` or `default_max_page_size`
```
So we're also adding a default max page size.
Note that the documentation mentioned that the default page size was 25.
However, before commit c984e666f, we were using a page size of 50 in
some cases. We're going with the one mentioned in the documentation
since we don't fully understand the old code.
5f80a75161