Customize broadcast queue and connection in config

[dhi2]

Created a pull request: #295

We need a custom queue and connection settings in the MessageWasSent file:
https://github.com/musonza/chat/blob/master/src/Eventing/MessageWasSent.php

(ref: https://laravel.com/docs/8.x/broadcasting#broadcast-queue)

This is because if I have the default QUEUE_CONNECTION=database in my .env then each time a message is sent it gets queued in the database, but I rather have it set to 'sync'.