Add metrics to get issues by label (#17201)

* Add metrics to get issues by label

* Add comment on IssueByLabelCount

* Code review - Unify "AS" in SQL (#17201)

* Code review - Remove useless join (#17201)

* Code review - Disable issue_by_label by default in settings (#17201)

* use e

* restore empty line

* update docs

Co-authored-by: 6543 <6543@obermui.de>
Co-authored-by: techknowlogick <matti@mdranta.net>
Co-authored-by: techknowlogick <techknowlogick@gitea.io>

modules/metrics/collector.go

@@ -24,6 +24,7 @@ type Collector struct {
 	Issues        *prometheus.Desc
 	IssuesOpen    *prometheus.Desc
 	IssuesClosed  *prometheus.Desc
+	IssuesByLabel *prometheus.Desc
 	Labels        *prometheus.Desc
 	LoginSources  *prometheus.Desc
 	Milestones    *prometheus.Desc
@@ -45,6 +46,7 @@ type Collector struct {
 
 // NewCollector returns a new Collector with all prometheus.Desc initialized
 func NewCollector() Collector {
+
 	return Collector{
 		Accesses: prometheus.NewDesc(
 			namespace+"accesses",
@@ -81,6 +83,11 @@ func NewCollector() Collector {
 			"Number of Issues",
 			nil, nil,
 		),
+		IssuesByLabel: prometheus.NewDesc(
+			namespace+"issues_by_label",
+			"Number of Issues",
+			[]string{"label"}, nil,
+		),
 		IssuesOpen: prometheus.NewDesc(
 			namespace+"issues_open",
 			"Number of open Issues",
@@ -177,7 +184,6 @@ func NewCollector() Collector {
 			nil, nil,
 		),
 	}
-
 }
 
 // Describe returns all possible prometheus.Desc
@@ -189,6 +195,7 @@ func (c Collector) Describe(ch chan<- *prometheus.Desc) {
 	ch <- c.Follows
 	ch <- c.HookTasks
 	ch <- c.Issues
+	ch <- c.IssuesByLabel
 	ch <- c.IssuesOpen
 	ch <- c.IssuesClosed
 	ch <- c.Labels
@@ -249,6 +256,14 @@ func (c Collector) Collect(ch chan<- prometheus.Metric) {
 		prometheus.GaugeValue,
 		float64(stats.Counter.Issue),
 	)
+	for _, il := range stats.Counter.IssueByLabel {
+		ch <- prometheus.MustNewConstMetric(
+			c.IssuesByLabel,
+			prometheus.GaugeValue,
+			float64(il.Count),
+			il.Label,
+		)
+	}
 	ch <- prometheus.MustNewConstMetric(
 		c.IssuesClosed,
 		prometheus.GaugeValue,