Alerting: Rule backtesting with experimental UI (#115525)

* add function to convert StateTransition to LokiEntry
* add QueryResultBuilder
* update backtesting to produce result similar to historian
* make shouldRecord public
* filter out noop transitions
* add experimental front-end
* add new fields
* move conversion of api model to AlertRule to validation
* add extra labels
* calculate tick timestamp using the same logic as in scheduler
* implement correct logic of calculating first evaluation timestamp
* add uid, group and folder uid they are needed for jitter strategy

* add JitterOffsetInDuration and JitterStrategy.String()

* add config `backtesting_max_evaluations` to [unified_alerting] (not documented for now)

* remove obsolete tests

* elevate permisisons for backtesting endpoint
* move backtesting to separate dir

pkg/services/ngalert/backtesting/eval_query.go

@@ -18,10 +18,13 @@ func (d *queryEvaluator) Eval(ctx context.Context, from time.Time, interval time
 		if err != nil {
 			return err
 		}
-		err = callback(idx, now, results)
+		cont, err := callback(idx, now, results)
 		if err != nil {
 			return err
 		}
+		if !cont {
+			break
+		}
 	}
 	return nil
 }