Enable Redis caching and queues for FreeScout.

Inspired by #4650.

• Ensure Redis server is installed.
• Ensure phpredis (not predis) module for PHP is installed. (Both PHP-FPM and the PHP cli!)
• Double-check your Redis settings in config/database.php. It must use phpredis, not predis.
• Add to your .env:

  CACHE_DRIVER=redis
  CACHE_PREFIX=freescout
  QUEUE_DRIVER=redis
  # Session drivers in FreeScout appear to be broken or incompatible with PHP 8. Only file and database drivers work.
  # SESSION_DRIVER=redis
  

• Activate the Redis Driver module.
• Run php artisan freescout:clear-cache.

When using PHP 8.4 you will see deprecation warnings, even when you have those disabled! This will interfere with your mail fetching!

This is a bug specific to PHP 8.4: php/php-src#17422

Please use PHP 8.1-8.3 or 8.5+.

You may start redis-cli and run KEYS freescout:* to check that the redis cache is being used.

• Why phpredis, not predis? Using phpredis requires us to install a driver in PHP only. This removes the maintenance burden that comes with adding predis to FreeScout.