Unified Alerting: Set max_attempts to 1 by default (#79095)

* Unified Alerting: Set `max_attempts` to 1 by default

The retry logic for unified alerting has been broken as far as v9.4.x, rather than fixing it in one go and causing a headache to our users with rules putting extra load on their datasources - I think a better approach is to simply set 1 as a default and then let our users change it.

I see two cons with this approach:

- Configuration for legacy to unified alerting cannot be ported over automatically, users will have to manually set `max_attempts` to 3 when migrating.
- Users expecting to get any sort of retrying (as with legacy alerting) will not have it out of the box and will have to manually edit the configuration.

Signed-off-by: gotjosh <josue.abreu@gmail.com>
---------

Signed-off-by: gotjosh <josue.abreu@gmail.com>

pkg/setting/setting_unified_alerting.go

@@ -47,7 +47,7 @@ const (
 	evaluatorDefaultEvaluationTimeout       = 30 * time.Second
 	schedulerDefaultAdminConfigPollInterval = time.Minute
 	schedulereDefaultExecuteAlerts          = true
-	schedulerDefaultMaxAttempts             = 3
+	schedulerDefaultMaxAttempts             = 1
 	schedulerDefaultLegacyMinInterval       = 1
 	screenshotsDefaultCapture               = false
 	screenshotsDefaultCaptureTimeout        = 10 * time.Second
@@ -294,15 +294,7 @@ func (cfg *Cfg) ReadUnifiedAlertingSettings(iniFile *ini.File) error {
 	}
 	uaCfg.EvaluationTimeout = uaEvaluationTimeout
 
-	uaMaxAttempts := ua.Key("max_attempts").MustInt64(schedulerDefaultMaxAttempts)
-	if uaMaxAttempts == schedulerDefaultMaxAttempts { // unified option or equals the default
-		legacyMaxAttempts := alerting.Key("max_attempts").MustInt64(schedulerDefaultMaxAttempts)
-		if legacyMaxAttempts != schedulerDefaultMaxAttempts {
-			cfg.Logger.Warn("falling back to legacy setting of 'max_attempts'; please use the configuration option in the `unified_alerting` section if Grafana 8 alerts are enabled.")
-		}
-		uaMaxAttempts = legacyMaxAttempts
-	}
-	uaCfg.MaxAttempts = uaMaxAttempts
+	uaCfg.MaxAttempts = ua.Key("max_attempts").MustInt64(schedulerDefaultMaxAttempts)
 
 	uaCfg.BaseInterval = SchedulerBaseInterval