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.

templates/admin/dashboard.tmpl

@@ -5,14 +5,6 @@
 				<p>{{(.locale.Tr "admin.dashboard.new_version_hint" .RemoteVersion AppVer) | Str2html}}</p>
 			</div>
 		{{end}}
-		<h4 class="ui top attached header">
-			{{.locale.Tr "admin.dashboard.statistic"}}
-		</h4>
-		<div class="ui attached segment">
-			<p>
-				{{.locale.Tr "admin.dashboard.statistic_info" .Stats.Counter.User .Stats.Counter.Org .Stats.Counter.PublicKey .Stats.Counter.Repo .Stats.Counter.Watch .Stats.Counter.Star .Stats.Counter.Action .Stats.Counter.Access .Stats.Counter.Issue .Stats.Counter.Comment .Stats.Counter.Oauth .Stats.Counter.Follow .Stats.Counter.Mirror .Stats.Counter.Release .Stats.Counter.AuthSource .Stats.Counter.Webhook .Stats.Counter.Milestone .Stats.Counter.Label .Stats.Counter.HookTask .Stats.Counter.Team .Stats.Counter.UpdateTask .Stats.Counter.Attachment | Str2html}}
-			</p>
-		</div>
 		<h4 class="ui top attached header">
 			{{.locale.Tr "admin.dashboard.operations"}}
 		</h4>

templates/admin/navbar.tmpl

@@ -53,6 +53,9 @@
 		<div class="item">
 			{{.locale.Tr "admin.monitor"}}
 			<div class="menu">
+				<a class="{{if .PageIsAdminMonitorStats}}active {{end}}item" href="{{AppSubUrl}}/admin/monitor/stats">
+					{{.locale.Tr "admin.monitor.stats"}}
+				</a>
 				<a class="{{if .PageIsAdminMonitorCron}}active {{end}}item" href="{{AppSubUrl}}/admin/monitor/cron">
 					{{.locale.Tr "admin.monitor.cron"}}
 				</a>

templates/admin/stats.tmpl

@@ -0,0 +1,17 @@
+{{template "admin/layout_head" (dict "ctxData" . "pageClass" "admin monitor")}}
+<div class="admin-setting-content">
+	<h4 class="ui top attached header">
+		{{.locale.Tr "admin.dashboard.statistic"}}
+	</h4>
+	<div class="ui attached table segment">
+		<table class="ui very basic striped table unstackable">
+			{{range $statsKey := .StatsKeys}}
+			<tr>
+				<td width="200">{{$statsKey}}</td>
+				<td>{{index $.StatsCounter $statsKey}}</td>
+			</tr>
+			{{end}}
+		</table>
+	</div>
+</div>
+{{template "admin/layout_footer" .}}