matomo.php returns HTTP 200 when unable to connect to redis

Nobody has claimed this yet.

If matomo is configured to use QueuedTracking with Redis as backend, and matomo.php is unable to connect to such Redis instance, HTTP 200 is returned.

I would expect matomo.php return !200. For monitoring the availability of the tracker API, it makes it harder to validate that the Tracker API is healthy.

The error msg that is returned:
```


Warning: Redis::connect(): connect() failed: Cannot assign requested address in /var/www/html/vendor/piwik/cache/src/Backend/Factory.php on line 60



Fatal error: Uncaught RedisException: Redis server went away in /var/www/html/vendor/piwik/cache/src/Backend/Factory.php:70
Stack trace:
#0 /var/www/html/vendor/piwik/cache/src/Backend/Factory.php(70): Redis->select(0)
#1 /var/www/html/vendor/piwik/cache/src/Backend/Factory.php(108): Piwik\Cache\Backend\Factory->buildRedisCache(Array)
#2 /var/www/html/core/Cache.php(75): Piwik\Cache\Backend\Factory->buildBackend('redis', Array)
#3 /var/www/html/config/global.php(67): Piwik\Cache::buildBackend('redis')
#4 [internal function]: DI\Definition\Source\DefinitionFile->{closure}(Object(DI\Container))
#5 /var/www/html/vendor/php-di/invoker/src/Invoker.php(82): call_user_func_array(Object(Closure), Array)
#6 /var/www/html/vendor/php-di/php-di/src/DI/Definition/Resolver/FactoryResolver.php(81): Invoker\Invoker->call(Object(Closure), Array)
#7 /var/www/html/vendor/php-di/php-di/src/DI/Definition/Resolver/ResolverDispatcher.php(58): DI\Definition\Resolver\FactoryResolver->resolve(Object(DI\Definition\FactoryDefinition), Array)
#8 /var in /var/www/html/vendor/piwik/cache/src/Backend/Factory.php on line 70
```

Headers returned:
```Request URL: X/matomo.php
Request Method: GET
Status Code: 200 ```

Start at matomo.php and trace the Redis failure through vendor/piwik/cache/src/Backend/Factory.php, core/Cache.php, and config/global.php. Reproduce a GET request with Redis unavailable and verify that the tracker returns a non-200 status instead of 200 when the connection fails.

Written by the indexing model from the issue text.