docs(logger): Add Example for LogDNA Transport

[dthyresson]

The logger documentation includes examples for how to use LogFlare and DataDog, but another popular transport is LogDNA.

This issue is a request to include how-to documentation in

See: https://github.com/redwoodjs/redwoodjs.com/blob/main/docs/logger.md

to setup LogDNA using the pino tranport.

// See: https://github.com/logdna/pino-logdna#api

const pinoLogdna = require('pino-logdna')
const opts = { /* pino options */ }
const stream = pinoLogdna({
   key: process.env.LOGDNA_INGESTION_KEY
 , onError: console.error
 })

// Logs now go to LogDNA
log.debug('Happy logging!') 
...