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/setting/setting_unified_alerting.go

@@ -156,6 +156,8 @@ type UnifiedAlertingSettings struct {
 
 	// AlertmanagerMaxTemplateOutputSize specifies the maximum allowed size for rendered template output in bytes.
 	AlertmanagerMaxTemplateOutputSize int64
+
+	BacktestingMaxEvaluations int
 }
 
 type RecordingRuleSettings struct {
@@ -594,6 +596,11 @@ func (cfg *Cfg) ReadUnifiedAlertingSettings(iniFile *ini.File) error {
 		return fmt.Errorf("setting 'alertmanager_max_template_output_bytes' is invalid, only 0 or a positive integer are allowed")
 	}
 
+	uaCfg.BacktestingMaxEvaluations = ua.Key("backtesting_max_evaluations").MustInt(100)
+	if uaCfg.BacktestingMaxEvaluations < 0 {
+		uaCfg.BacktestingMaxEvaluations = 100
+	}
+
 	cfg.UnifiedAlerting = uaCfg
 	return nil
 }