Handle postgres notices

It seems like libpq by default sends notices to the terminal, which leads to a lot of logs, e.g. in testing:

NOTICE:  drop cascades to 2 other objects
DETAIL:  drop cascades to table person
drop cascades to table post

postgresql-libpq provides enableNoticeReporting/disableNoticeReporting, but they operate on postgresql-libpq's Connection type, which withPostgresqlPool (and co) don't directly expose.

A workaround would be to call postgresql-simple.connect directly and call disableNoticeReporting and use openSimpleConn, but it doesn't seem straightforward to get back a Pool SqlBackend.

The approach that makes the most sense to me is to use the MonadLogger instance and send notice reportings through the logger function. Something like

open' modConn getVer cstr logFunc = do
    conn <- PG.connectPostgreSQL cstr

    {- add this -}
    enableNoticeReporting conn
    let noticeLoop = getNotice conn >>= \case
            Just bs -> logFunc ... bs >> noticeLoop
            Nothing -> return ()
    forkIO noticeLoop
    {- end -}

    modConn conn
    ver <- getVer conn
    smap <- newIORef $ Map.empty
    return $ createBackend logFunc ver smap conn

Start by locating the PostgreSQL backend entry points around withPostgresqlPool, open', and createBackend, then read how the MonadLogger function is passed through connection setup. Review the postgresql-libpq notice APIs and determine how notices should reach the logger without being printed to the terminal. Done means notices are handled through the logger while pooled connections continue to work.