Use a separate admin page to show global stats, remove actions stat (#25062)

Before, Gitea shows the database table stats on the `admin dashboard`
page.

It has some problems:

* `count(*)` is quite heavy. If tables have many records, this blocks
loading the admin page blocks for a long time
* Some users had even reported issues that they can't visit their admin
page because this page causes blocking or `50x error (reverse proxy
timeout)`
* The `actions` stat is not useful. The table is simply too large. Does
it really matter if it contains 1,000,000 rows or 9,999,999 rows?
* The translation `admin.dashboard.statistic_info` is difficult to
maintain.

So, this PR uses a separate page to show the stats and removes the
`actions` stat.


![image](https://github.com/go-gitea/gitea/assets/2114189/babf7c61-b93b-4a62-bfaa-22983636427e)

## ⚠️ BREAKING

The `actions` Prometheus metrics collector has been removed for the
reasons mentioned beforehand.
Please do not rely on its output anymore.

routers/web/admin/admin.go

@@ -8,11 +8,13 @@ import (
 	"fmt"
 	"net/http"
 	"runtime"
+	"sort"
 	"time"
 
 	activities_model "code.gitea.io/gitea/models/activities"
 	"code.gitea.io/gitea/modules/base"
 	"code.gitea.io/gitea/modules/context"
+	"code.gitea.io/gitea/modules/json"
 	"code.gitea.io/gitea/modules/setting"
 	"code.gitea.io/gitea/modules/updatechecker"
 	"code.gitea.io/gitea/modules/web"
@@ -26,6 +28,7 @@ const (
 	tplQueue       base.TplName = "admin/queue"
 	tplStacktrace  base.TplName = "admin/stacktrace"
 	tplQueueManage base.TplName = "admin/queue_manage"
+	tplStats       base.TplName = "admin/stats"
 )
 
 var sysStatus struct {
@@ -111,7 +114,6 @@ func updateSystemStatus() {
 func Dashboard(ctx *context.Context) {
 	ctx.Data["Title"] = ctx.Tr("admin.dashboard")
 	ctx.Data["PageIsAdminDashboard"] = true
-	ctx.Data["Stats"] = activities_model.GetStatistic()
 	ctx.Data["NeedUpdate"] = updatechecker.GetNeedUpdate()
 	ctx.Data["RemoteVersion"] = updatechecker.GetRemoteVersion()
 	// FIXME: update periodically
@@ -126,7 +128,6 @@ func DashboardPost(ctx *context.Context) {
 	form := web.GetForm(ctx).(*forms.AdminDashboardForm)
 	ctx.Data["Title"] = ctx.Tr("admin.dashboard")
 	ctx.Data["PageIsAdminDashboard"] = true
-	ctx.Data["Stats"] = activities_model.GetStatistic()
 	updateSystemStatus()
 	ctx.Data["SysStatus"] = sysStatus
 
@@ -153,3 +154,30 @@ func CronTasks(ctx *context.Context) {
 	ctx.Data["Entries"] = cron.ListTasks()
 	ctx.HTML(http.StatusOK, tplCron)
 }
+
+func MonitorStats(ctx *context.Context) {
+	ctx.Data["Title"] = ctx.Tr("admin.monitor.stats")
+	ctx.Data["PageIsAdminMonitorStats"] = true
+	bs, err := json.Marshal(activities_model.GetStatistic().Counter)
+	if err != nil {
+		ctx.ServerError("MonitorStats", err)
+		return
+	}
+	statsCounter := map[string]any{}
+	err = json.Unmarshal(bs, &statsCounter)
+	if err != nil {
+		ctx.ServerError("MonitorStats", err)
+		return
+	}
+	statsKeys := make([]string, 0, len(statsCounter))
+	for k := range statsCounter {
+		if statsCounter[k] == nil {
+			continue
+		}
+		statsKeys = append(statsKeys, k)
+	}
+	sort.Strings(statsKeys)
+	ctx.Data["StatsKeys"] = statsKeys
+	ctx.Data["StatsCounter"] = statsCounter
+	ctx.HTML(http.StatusOK, tplStats)
+}