Transactions in schema-only mode
### Summary

If I try to use an connected client to run my own graphql in the API (schema-only mode) and use withPostGraphileContext, I get an exception when postgraphile calls client.connect().  What is the best way to bring my own client / transaction and run a graphql?

I wonder, why does withPostGraphileContext accept a pgPool and not a pgConfig like createPostGraphileSchema?   

https://www.graphile.org/postgraphile/usage-schema/#api-withpostgraphilecontextoptions-callback 

thank you.