This change is an initial step to change JWT aud configuration to regular expression.
Exporting function
audMatchesCfg :: AppConfig -> Text -> Bool
from Config module allows changing the way how JWT aud is configured to be isolated and not affect code in Auth.JWT
This change introduces a PostgREST.Auth.Jwt module containing JWT validation functions.
The reason to extract them from Auth is to enable JwtCache module to reuse them without introducing module dependency cycle.