Make MediaProxy failure tracking less brutal

The current failure tracking mechanism will never request anything that didn't respond with a success, 403, 404, or 5xx codes. This is causing issues when using in real fediverse because of weird status codes some software has and timeouts being frequent. This patch changes failure tracking mechanism to only never request the url again if it responded with 400, 204, or the body is too large, otherwise it can be re-requested in 60 seconds.