Add graphile behavior debug command to behavior docs

[jcgsville]

The following doc should probably briefly mention that npx graphile behavior debug exists for sponsors. Knowing of the existence of that command would have helped me reason about behavior stuff faster. I imagine it would do the same for other sponsors.

https://postgraphile.org/postgraphile/next/behavior

Happy to make the PR after a 👍

[benjie]

I'm surprised it doesn't already exist! Please go ahead and add it. I really need to make it so that the "applying defaults" phase isn't shown through its current "multiplication" though, that's really confusing for users.

[jcgsville]

👍 I'll add a lil callout that it's WIP or something