toStartOfIntervalFunction Aligns Hour Intervals to Midnight

The toStartOfIntervalFunction will align hour intervals to the midnight (in previous versions they were aligned to the start of unix epoch). For example, toStartOfInterval(x, INTERVAL 11 HOUR) will split every day into three intervals: 00:00:00..10:59:59, 11:00:00..21:59:59 and 22:00:00..23:59:59. This behaviour is more suited for practical needs. This closes #9510. #22060 (alexey-milovidov).