Port over new DB features

[grossvogel]

1. Allow the Postgres instance size to be customized in the review config
2. Allow the review config to specify Postgres extensions to install during DB init

https://github.com/revelrylabs/review_bot/pull/94

[grossvogel]

@vaxinate is working on updating the DB script to copy all schemas from the source database, as well. That might fit well into this issue unless it turns out to be a huge change.

https://github.com/revelrylabs/review_bot/issues/101

[vaxinate]

I'm expecting my changes to either simply be changing the kubedb init script so that pg_dump gets all the schemas, or I'm going to add options to the .review_bot.yml file for specifying which schemas to dump out (and restore). I don't expect either thing to take too much in the way of gymnastics.