* Adds query stat handler,
for query and query_range api, victoriametrics tracks query execution time,
stats are expored at /api/v1/status/queries endpoint with topN param
https://github.com/VictoriaMetrics/VictoriaMetrics/issues/907
* fixed query stats bugs
* improves queryStats tracker
* improves query stat
* small fix
* fix tests
* added more tests
* fixes 386 tests
* naming fixes
* adds drop for outdated records
