Alerting: Add rule_query_offset setting for Prometheus rule conversion (#102500)

Adds a new configuration option to specify a time offset for rule evaluation, which gets applied and saved during the Prometheus -> Grafana conversion. For example:

[unified_alerting.prometheus_conversion]
rule_query_offset = 1m

Changing this option affects only the rules imported after the change. If query_offset is set at the group level, it takes precedence over this setting.

Default is set to 1m.

pkg/setting/setting_unified_alerting.go

@@ -112,6 +112,7 @@ type UnifiedAlertingSettings struct {
 	StateHistory                  UnifiedAlertingStateHistorySettings
 	RemoteAlertmanager            RemoteAlertmanagerSettings
 	RecordingRules                RecordingRuleSettings
+	PrometheusConversion          UnifiedAlertingPrometheusConversionSettings
 
 	// MaxStateSaveConcurrency controls the number of goroutines (per rule) that can save alert state in parallel.
 	MaxStateSaveConcurrency    int
@@ -165,6 +166,12 @@ type UnifiedAlertingReservedLabelSettings struct {
 	DisabledLabels map[string]struct{}
 }
 
+// UnifiedAlertingPrometheusConversionSettings contains configuration for converting Prometheus rules to Grafana format
+type UnifiedAlertingPrometheusConversionSettings struct {
+	// RuleQueryOffset defines a time offset to apply to rule queries during conversion from Prometheus to Grafana format
+	RuleQueryOffset time.Duration
+}
+
 type UnifiedAlertingStateHistorySettings struct {
 	Enabled       bool
 	Backend       string
@@ -437,6 +444,11 @@ func (cfg *Cfg) ReadUnifiedAlertingSettings(iniFile *ini.File) error {
 	}
 	uaCfg.StateHistory = uaCfgStateHistory
 
+	prometheusConversion := iniFile.Section("unified_alerting.prometheus_conversion")
+	uaCfg.PrometheusConversion = UnifiedAlertingPrometheusConversionSettings{
+		RuleQueryOffset: prometheusConversion.Key("rule_query_offset").MustDuration(time.Minute),
+	}
+
 	rr := iniFile.Section("recording_rules")
 	uaCfgRecordingRules := RecordingRuleSettings{
 		Enabled:              rr.Key("enabled").MustBool(false),