Pull request: querylog: more opt

Updates 1273.

Squashed commit of the following:

commit 167c0b5acaab8a2676de2cea556c861dc0efbc72
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Mon Apr 12 18:12:43 2021 +0300

    querylog: imp naming

commit 5010ad113e46335011a721cbcc9fc9b1fc623722
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Mon Apr 12 17:53:41 2021 +0300

    querylog: more opt

internal/querylog/querylogfile.go

@@ -118,7 +118,7 @@ func (l *queryLog) readFileFirstTimeValue() int64 {
 	}
 	buf = buf[:r]
 
-	val := readJSONValue(string(buf), "T")
+	val := readJSONValue(string(buf), `"T":"`)
 	t, err := time.Parse(time.RFC3339Nano, val)
 	if err != nil {
 		return -1