Add support of crontab-like settings

[umputun]

Probably we need it on the top level as well on each provider/check level. The goal is to "fake" the actual check if it fail outside of the allowed hours/days. This functionality is useful for services/endpoints/whatever we want to monitor some hours/days only. For example some endpoints may not produce the same result after business day other, some may produce different result at night and so on