Alerting: Add a "Reason" to Alert Instances to show underlying cause of state. (#49259)

This change adds a field to state.State and models.AlertInstance
that indicate the "Reason" that an instance has its current state. This
helps us account for cases where the state is "Normal" but the
underlying evaluation returned "NoData" or "Error", for example.

Fixes #42606

Signed-off-by: Joe Blubaugh <joe.blubaugh@grafana.com>

pkg/services/ngalert/models/instance.go

@@ -12,6 +12,7 @@ type AlertInstance struct {
 	Labels            InstanceLabels
 	LabelsHash        string
 	CurrentState      InstanceStateType
+	CurrentReason     string
 	CurrentStateSince time.Time
 	CurrentStateEnd   time.Time
 	LastEvalTime      time.Time
@@ -49,6 +50,7 @@ type SaveAlertInstanceCommand struct {
 	RuleUID           string
 	Labels            InstanceLabels
 	State             InstanceStateType
+	StateReason       string
 	LastEvalTime      time.Time
 	CurrentStateSince time.Time
 	CurrentStateEnd   time.Time
@@ -66,23 +68,12 @@ type GetAlertInstanceQuery struct {
 
 // ListAlertInstancesQuery is the query list alert Instances.
 type ListAlertInstancesQuery struct {
-	RuleOrgID int64 `json:"-"`
-	RuleUID   string
-	State     InstanceStateType
+	RuleOrgID   int64 `json:"-"`
+	RuleUID     string
+	State       InstanceStateType
+	StateReason string
 
-	Result []*ListAlertInstancesQueryResult
-}
-
-// ListAlertInstancesQueryResult represents the result of listAlertInstancesQuery.
-type ListAlertInstancesQueryResult struct {
-	RuleOrgID         int64             `xorm:"rule_org_id" json:"ruleOrgId"`
-	RuleUID           string            `xorm:"rule_uid" json:"ruleUid"`
-	Labels            InstanceLabels    `json:"labels"`
-	LabelsHash        string            `json:"labeHash"`
-	CurrentState      InstanceStateType `json:"currentState"`
-	CurrentStateSince time.Time         `json:"currentStateSince"`
-	CurrentStateEnd   time.Time         `json:"currentStateEnd"`
-	LastEvalTime      time.Time         `json:"lastEvalTime"`
+	Result []*AlertInstance
 }
 
 // ValidateAlertInstance validates that the alert instance contains an alert rule id,