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.
We accidentally removed this code in commit c984e666f. As mentioned in
our GraphQL documentation, limiting the depth of the queries helps
against DoS attacks.
