Replace `psycopg2` with `psycopg2-binary`?

[grahamalama]

I'm opening this issues as a venue of discussion about whether we should replace psycopg2 with psycopg2-binary in this repo.

In #2942, we replaced psycopg-binary with psycopg2 in requirements.txt, since kinto[postgresql] requires psycopg2 specifically.

In the comments of that PR, we proposed to instead replace psycopg2 with psycopg-binary in requirements.txt and the dependencies of the postgresql extra. Doing so would make kinto builds even faster.

However, the psycopg2 documentation has some warnings about using psycopg2-binary in production.

TBD: which version of psycopg2 should we use in this repo?