Investigate satement_timeout for read only queries

[s4ke]

https://www.postgresql.org/docs/9.6/runtime-config-client.html

If we set this for read only queries, this could help stability if for whatever reason a custom filter via the new filter support in 2.1.0 causes performance degradation.

[s4ke]

transaction_timeout is maybe more what we want for requests?

We probably want to undo this after every request is finished. It's important to not break any existing client pooling.