docs: fix the docs to correctly represent the config as milliseconds

[pahnin]

• current docs are incorrect because it should be either 15s or 15000
• postgres suggests to use milliseconds format in postgres docs, since we just carry forward this value to DB server it just confuses people on what to use

[mefellows]

Seems reasonable to me. I'm still confused how 15s works though if it is supposed to accept millis!

[pahnin]

https://github.com/search?q=repo%3Apostgres%2Fpostgres+statement_timeout&type=code&p=1

postgres accepts both