Move database config validation out of config

[jisantuc]

To check to make sure that the database parameters can actually be used to connect to a database,
right now the JVM app calls .validate from decline and unsafely runs a quick query right now to see if it
succeeds.

However, this is impossible on JS -- unsafeRunSync doesn't exist on IO in scala.js, and you can't call Await.result on a future https://www.scala-js.org/doc/project/linking-errors.html#using-blocking-apis-eg-awaitresult

This effect could pretty easily be moved out to app startup instead, which I think would let both apps verify connectivity before they
fully start up.