Optimize Caching

Adding certain caches into APCu, as it may be faster than Redis and contains the basic building blocks for the code:

$settings['cache']['bins']['bootstrap'] = 'cache.backend.chainedfast';
$settings['cache']['bins']['discovery'] = 'cache.backend.chainedfast';
$settings['cache']['bins']['config'] = 'cache.backend.chainedfast';
$settings['cache']['bins']['container'] = 'cache.backend.chainedfast';

Change Record: New cache backend configuration order, per-bin default before default configuration

Is there a way in settings.php to know if the site is installed, i.e. if Redis is available, or not.