Postgraphile: Have poolOrConfig throw if invalid

[benjie]

In the final fallback poolOrConfig || {}:

https://github.com/postgraphql/postgraphql/blob/233f55c53f8c982cb566b48b63e0fa5bcc7ed1fd/src/postgraphql/postgraphql.ts#L83-L92

we should check that poolOrConfig is a simple object (and not, for example, a pool returned from a different version of the pg module 😡 ) and throw with a helpful error if not.

[MaxDesiatov]

Just stumbled upon this myself, a documentation page has pg-pool as an example, which isn't an instance of Pool from pg module, which causes errors. That documentation page should be fixed as well.

[benjie]

We have quacksLikePgPool now; so due to this duck-typing this shouldn't be an issue any more.