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/classic/classic.go

@@ -5,6 +5,7 @@ import (
 	"encoding/json"
 	"fmt"
 	"strconv"
+	"time"
 
 	"github.com/grafana/grafana-plugin-sdk-go/data"
 
@@ -67,7 +68,7 @@ func (cmd *ConditionsCmd) NeedsVars() []string {
 
 // Execute runs the command and returns the results or an error if the command
 // failed to execute.
-func (cmd *ConditionsCmd) Execute(_ context.Context, vars mathexp.Vars) (mathexp.Results, error) {
+func (cmd *ConditionsCmd) Execute(_ context.Context, _ time.Time, vars mathexp.Vars) (mathexp.Results, error) {
 	firing := true
 	newRes := mathexp.Results{}
 	noDataFound := true