Alerting: Make context deadline on AlertNG service startup configurable (#96053)

* Make alerting context deadline configurable

* Remove debug logs

* Change default timeout

* Update tests

pkg/setting/setting_unified_alerting.go

@@ -45,6 +45,7 @@ const (
 	}
 }
 `
+	alertingDefaultInitializationTimeout    = 30 * time.Second
 	evaluatorDefaultEvaluationTimeout       = 30 * time.Second
 	schedulerDefaultAdminConfigPollInterval = time.Minute
 	schedulerDefaultExecuteAlerts           = true
@@ -90,6 +91,7 @@ type UnifiedAlertingSettings struct {
 	HARedisMaxConns                 int
 	HARedisTLSEnabled               bool
 	HARedisTLSConfig                dstls.ClientConfig
+	InitializationTimeout           time.Duration
 	MaxAttempts                     int64
 	MinInterval                     time.Duration
 	EvaluationTimeout               time.Duration
@@ -229,6 +231,11 @@ func (cfg *Cfg) ReadUnifiedAlertingSettings(iniFile *ini.File) error {
 		uaCfg.DisabledOrgs[orgID] = struct{}{}
 	}
 
+	uaCfg.InitializationTimeout, err = gtime.ParseDuration(valueAsString(ua, "initialization_timeout", (alertingDefaultInitializationTimeout).String()))
+	if err != nil {
+		return err
+	}
+
 	uaCfg.AdminConfigPollInterval, err = gtime.ParseDuration(valueAsString(ua, "admin_config_poll_interval", (schedulerDefaultAdminConfigPollInterval).String()))
 	if err != nil {
 		return err