Chore: Expression engine to support relative time range (#57474)

* make TimeRange interface and add relative range
* make Execute methods support the current time
* update resample to support relative time range
* update DSNode to support relative time range
* update query service to create queries with absolute time
* make alerting evaluator create relative time ranges

pkg/expr/threshold_test.go

@@ -93,7 +93,6 @@ func TestUnmarshalThresholdCommand(t *testing.T) {
 			RefID:      "",
 			Query:      qmap,
 			QueryType:  "",
-			TimeRange:  TimeRange{},
 			DataSource: nil,
 		})