[Alerting]: Extend quota service to optionally set limits on alerts (#33283)

* Quota: Extend service to set limit on alerts

* Add test for applying quota to alert rules

* Apply suggestions from code review

Co-authored-by: Diana Payton <52059945+oddlittlebird@users.noreply.github.com>

* Get used alert quota only if naglert is enabled

* Set alert limit to zero if nglalert is not enabled
Co-authored-by: Diana Payton <52059945+oddlittlebird@users.noreply.github.com>

pkg/setting/setting_quota.go

@@ -9,6 +9,7 @@ type OrgQuota struct {
 	DataSource int64 `target:"data_source"`
 	Dashboard  int64 `target:"dashboard"`
 	ApiKey     int64 `target:"api_key"`
+	AlertRule  int64 `target:"alert_rule"`
 }
 
 type UserQuota struct {
@@ -22,6 +23,7 @@ type GlobalQuota struct {
 	Dashboard  int64 `target:"dashboard"`
 	ApiKey     int64 `target:"api_key"`
 	Session    int64 `target:"-"`
+	AlertRule  int64 `target:"alert_rule"`
 }
 
 func (q *OrgQuota) ToMap() map[string]int64 {
@@ -64,12 +66,19 @@ func (cfg *Cfg) readQuotaSettings() {
 	quota := cfg.Raw.Section("quota")
 	Quota.Enabled = quota.Key("enabled").MustBool(false)
 
+	var alertOrgQuota int64
+	var alertGlobalQuota int64
+	if cfg.IsNgAlertEnabled() {
+		alertOrgQuota = quota.Key("org_alert_rule").MustInt64(100)
+		alertGlobalQuota = quota.Key("global_alert_rule").MustInt64(-1)
+	}
 	// per ORG Limits
 	Quota.Org = &OrgQuota{
 		User:       quota.Key("org_user").MustInt64(10),
 		DataSource: quota.Key("org_data_source").MustInt64(10),
 		Dashboard:  quota.Key("org_dashboard").MustInt64(10),
 		ApiKey:     quota.Key("org_api_key").MustInt64(10),
+		AlertRule:  alertOrgQuota,
 	}
 
 	// per User limits
@@ -85,6 +94,7 @@ func (cfg *Cfg) readQuotaSettings() {
 		Dashboard:  quota.Key("global_dashboard").MustInt64(-1),
 		ApiKey:     quota.Key("global_api_key").MustInt64(-1),
 		Session:    quota.Key("global_session").MustInt64(-1),
+		AlertRule:  alertGlobalQuota,
 	}
 
 	cfg.Quota = Quota